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NOTICE OF INCORPORATION 

United States Legal Document 

J^" All citizens and residents are hereby advised that 
this is a legally binding document duly incorporated by 
reference and that failure to comply with such 
requirements as hereby detailed within may subject you 
to criminal or civil penalties under the law. Ignorance of 
the law shall not excuse noncompliance and it is the 
responsibility of the citizens to inform themselves as to 
the laws that are enacted in the United States of America 
and in the states and cities contained therein. "^& 

* * 

IEEE C2 (2002), the National Electrical Safety 
Code, as incorporated by and mandated in the 
States and Municipalities, including 4 Code of 
Colorado Regulations 723, Rule 2334 and by 
Rule 25-24.515 of the Florida Administrative Code. 






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Published by the Institute of Electrical and Electronics Engineers, Inc. 



Accredited 

Standards 

Committee 

C2-2002 



National Electrical Safety Code® 

Secretariat 
Institute of Electrical and Electronics Engineers, Inc. 

Approved 5 February 2001 
Institute of Electrical and Electronics Engineers, Inc. 

Approved 14 June 2001 
American National Standards Institute 



2002 Edition 

2nd Printing 

Corrected Edition 

5 August 2002 

Abstract: This standard covers basic provisions for safeguarding of persons from hazards arising from the installation, 
operation, or maintenance of 1) conductors and equipment in electric supply stations, and 2) overhead and underground 
electric supply and communication lines. It also includes work rules for the construction, maintenance, and operation of 
electric supply and communication lines and equipment. 

The standard is applicable to the systems and equipment operated by utilities, or similar systems and equipment, of an 
industrial establishment or complex under the control of qualified persons. 

This standard consists of the introduction, definitions, grounding rules, list of referenced and bibliographic documents, 
and Parts 1, 2, 3, and 4 of the 2002 Edition of the National Electrical Safety Code. 

Keywords: communications industry safety; construction of communication lines; construction of electric supply lines; 
electrical safety; electric supply stations; electric utility stations; high-voltage safety; operation of communications sys- 
tems; operation of electric supply systems; power station equipment; power station safety; public utility safety; safety 
work rules; underground communication line safety; underground electric line safety 



1 August 2001 



The Institute of Electrical and Electronics Engineers, Inc. 
3 Park Avenue, New York, NY 10016-5997, USA 

Copyright © 2001 by the 
Institute of Electrical and Electronics Engineers, Inc. 

All rights reserved. Published 2001 
Printed in the United States of America 

National Electrical Safety Code® and NESC® are registered trademarks and 

service marks of the Institute of Electrical and Electronics Engineers, Inc. 

The NESC logo is a trademark of the Institute of Electrical and Electronics Engineers. 

The National Electrical Code® and NEC® are registered trademarks of 

the National Fire Protection Association. 

ISBN 0-7381-2778-7 

Public authorities are granted permission to republish the material 

herein in laws, regulations, administrative orders, ordinances, or 

similar documents. No other party may reproduce in any form, in an 

electronic retrieval system or otherwise, any portion of this document, 

without the prior written permission of the publisher. 



SH94911 



Recognized as an 
American National Standard 



An American National Standard implies a consensus of those substantially concerned 
with its scope and provisions. An American National Standard is intended as a guide to 
aid the manufacturer, the consumer, and the general public. The existence of an Amer- 
ican National Standard does not in any respect preclude anyone, whether he has ap- 
proved the standard or not, from manufacturing, marketing, purchasing, or using 
products, processes, or procedures not conforming to the standard. American National 
Standards are subject to periodic review and users are cautioned to obtain the latest 
editions. 



Foreword 

(This foreword is not a part of Accredited Standards Committee C2-2002, National Electrical Safety Code .) 

This publication consists of the parts of the National Electrical Safety Code® (NESC®) currently in effect. 
The former practice of designating parts by editions has not been practical for some time. In the 1977 Edition, 
Parts 1 and 4 were 6th Editions; Part 2 was a 7th Edition; Part 3 was a revision of the 6th Edition; Part 2, 
Section 29, did not cover the same subject matter as the 5th Edition; and Part 3 was withdrawn in 1970. In 
the 1987 Edition, revisions were made in all parts, and revisions to all parts have been made in subsequent 
editions. It is therefore recommended that reference to the NESC be made solely by the year of the published 
volume and desired part number. Separate copies of the individual parts are not available. 

Work on the NESC started in 1913 at the National Bureau of Standards (NBS), resulting in the publication 
of NBS Circular 49. The last complete edition of the Code (the 5th Edition, NBS Handbook H30) was issued 
in 1948, although separate portions had been available at various times starting in 1938. Part 2— Definitions, 
and the Grounding Rules, 6th Edition, was issued as NBS Handbook H81, ANSI C2.2-1960, in November 
1961 , but work on other parts was not actively in process again until 1970. 

In 1970 the C2 Committee decided to delete the Rules for the Installation and Maintenance of Electric 
Utilization Equipment (Part 3 of the 5th Edition), now largely covered by the National Electrical Code (ANSI/ 
NFPA 70), and the Rules for Radio Installations (Part 5 of the 5th Edition) from future editions. The 
Discussion of the NESC, issued as NBS Handbook H4 (1928 Edition) for the 4th Edition of the NESC and 
as NBS Handbook H39 for Part 2 of the Grounding Rules of the 5th Edition, was not published for the 6th 
Edition. 

The 1981 Edition included major changes in Parts 1, 2, and 3, minor changes in Part 4, and the 
incorporation of the rules common to all parts into Section 1. The 1984 Edition was revised to update all 
references and to list those references in a new Section 3. Rounded metric values, for information only, were 
added. Gender-related terminology was deleted. Section 1 —Introduction, Section 2— Definitions, 
Section 3 — References , and Section 9 — Grounding Methods , were made applicable to each of the Parts 1,2, 
3, and 4. 

The 1987 Edition was revised extensively. Definitions were changed or added. Requirements affecting 
grounding methods, electric supply stations, overhead line clearances and loading, underground lines, and 
work rules were revised. 

The 1990 Edition included several major changes. General rules were revised. A significant change to the 
method for specifying overhead line clearances was made and the rationale added as Appendix A. 
Requirements for clearances of overhead lines from grain bins and an alternate method for determining the 
strength requirements for wood structures was added. Rules covering grounding methods, electric supply 
stations, underground lines, and work rules were changed. 

In the 1993 Edition, changes were made in the rules applicable to emergency and temporary installations. 
In Section 9 and Parts 1, 2, and 3, rules were extended or clarified to include HVDC systems. The 
requirements for random separation of direct-buried supply and communication systems were modified for 
consistency and clarity, as was the rule in Part 4 on tagging electric supply circuits. 

In the 1997 edition, the most notable general change that took place is that numerical values in the metric 
(SI) system are shown in the preferred position, with customary inch-foot-pound values (inside parentheses) 
following. A bibliography, Appendix B, which consists of a list of resources identified in notes or 
recommendations, was added. Changes were made to rules affecting grounding, electric supply stations, and 
overhead lines, particularly with regard to clearance rules applicable to emergency and temporary 
installations. Strength requirements contained in Sections 24, 25, and 26 were revised completely. 
Underground line requirements for random separation for underground lines of direct-buried cables were 
modified. The requirement for cable identification marking by means of sequentially placed logos was 
introduced. Work rules added a requirement that warning signs and tags comply with applicable ANSI 
standards, tagging requirements were clarified with regard to SCAD A, and extensive requirements for fall 
protection were added. 

In the 2002 Edition, several changes were made that affected all or several parts of the Code. Particularly, 
this edition clarifies interfaces between the NEC and NESC with regard to Code jurisdiction in the area of 
street lights and area lights. Also included is clarification for situations between utility workers and their 

iii 
Copyright © 2001 IEEE. All rights reserved. 



I 



authorized contractors and installations on industrial complexes. 

In Section 2, definitions for communication lines, de-energized, fiber-optic cable— communications, 
fiber-optic cable— supply, readily climbable supporting structures, and vault were either modified or added. 

No changes were made in the 2002 Edition regarding use of earth or sea as a continuous conductor in 
HVDC systems. Subcommittee 1 reviewed a change proposal with regard to using earth or sea as a continuous 
conductor and did not see an immediate need to revise the NESC for this type of operation for HVDC systems 
in the United States. Although several systems in Europe and one in the Philippines currently use sea as a 
conductor, there are concerns that should be addressed before revising the Code. The subcommittee 
recognized the comments submitted by members of the IEEE Power Engineering Society Substations 
Committee and Transmission and Distribution Committee, the work accomplished within joint working 
groups in IEEE and NACE International, and further endorsements received from recognized HVDC experts. 
If there is desire by some to design and install a monopolar system, it is permissible under Rule 013A2 to do 
so as an experimental system. The subcommittee also recommended that any such system be limited to using 
sea, not land, as a sole conductor for any part of the circuit. 

In Section 9— Grounding Methods, a new rule was added to cover grounding requirements for a 
communication entity that wishes to use its own separate ground electrode. This requires that the 
communication ground be bonded with the grounding electrode conductor of the supply system to assure 
equal potential between the two systems. 

In Part 1 —Electric Supply Stations, the rules were clarified to be applicable to both ac and dc circuits. DC 
station clearances were added to the appropriate table. Requirements were revised to allow exceptions from 
prohibiting storage of equipment within an electrical supply station . The exception allows storage of material 
essential for maintenance and temporary storage of material related to work in progress in the station or a 
nearby transmission line. Restrictions are required to maintain safe clearances and working conditions. A 
Tentative Interim Amendment (TIA) was approved to remove the implication that grounding may be omitted 
when working on conductors normally operating at 25 kV or less where a visible open switch exists. The 
statement is not applicable to Part 1 , and it may be a leftover practice that is no longer valid. 

In Part 2— Overhead Lines, additional wording was added to address the situation of supply workers 
working in close proximity to communication antennas. New wording was also added to cover clearance of 
line conductors from communication antennas, and to clarify clearances of conductors from grain bins, boat 
launching areas, service drops, support arms, and lighting luminaires. Clarification was added to relationship 
of approach distances for non-utility workers from overhead lines and associated equipment. A major revision 
to Sections 25 and 26 on Strength and Loadings has begun and will span at least 3 Code cycles by the time it 
is completed. This is due to more sophisticated structural calculations that will be required, e.g., Load and 
Resistance Factor Design (LRFD), updated and improved input data from new wind and ice maps, and new 
pole materials that will supplement wood. Some change proposals were incorporated into the 2002 edition; 
others will be deferred until a later edition when the industry has become more familiar with the nature of 
these changes. For this edition, proposals were accepted to 1) treat wood, steel, and concrete poles with 
consistent Overhead Factors, and 2) include a new Extreme Wind Map that uses a new 3-s gust criteria, 
replacing the existing fastest mile wind. In addition, expanded calculations are required due to the use of gust 
response factor, importance factor, and velocity pressure coefficient. 

In Part 3— Underground Lines, the requirements for random separation changed to prohibit both 
communication lines and power from being any closer than 12 in from fuel or steam lines. Other new rules 
address location of pad-mounted equipment and pedestals and cable protection by means of climbing devices 
required to be installed within the manhole. Also included are revised rules on burial depth for streetlight 
cables and security of above ground equipment. 

In Part 4— Work Rules, the maximum use voltage rating of rubber protective equipment was added as a 
requirement. 

Substantive changes in the 2002 edition are identified by a bar in the left-hand margin. In several cases, 
rules have been relocated without substantive changes in the wording. In these cases, only the rule numbers 
have been indicated as having been changed. 

The Institute of Electrical and Electronics Engineers, Inc. was designated as the administrative secretariat 
for C2 in January 1973, assuming the functions formerly performed by the National Bureau of Standards. 

Comments on the rules and suggestions for their improvement are invited, especially from those who have 
experience in their practical application. In future editions every effort will be made to improve the rules, both 

iv 
Copyright © 2001 IEEE. All rights reserved. 



m 
m 

w in the adequacy of coverage and in the clarification of requirements. Comments should be addressed to: 

m 

^ Secretary 

™ National Electrical Safety Code Committee 

£} Institute of Electrical and Electronics Engineers , Inc . 

^ 445 Hoes Lane 

9 P.O. Box 1331 

A Piscataway, NJ 08855-1331 

A representative Committee on Interpretations has been established to prepare replies to requests for 

™ interpretation of the rules contained in the Code. Requests for interpretation should state the rule in question, 

£) as well as the conditions under which it is being applied. Interpretations are intended to clarify the intent of 

— specific rules and are not intended to supply consulting information on the application of the Code. Requests 

^ for interpretation should be sent to the address above. 

(B If the request is suitable for processing , it will be sent to the Interpretations Committee . After consideration 

am by the committee, which may involve many exchanges of correspondence, the inquirer will be notified of its 

decision. Decisions are published regularly and may be ordered or accessed online at no cost at http:// 

w standards.ieee.org/nesc. 

ttk The NESC as written is a voluntary standard. However, some editions and some parts of the Code have 

,_ been adopted, with and without changes, by some state and local jurisdictional authorities. To determine the 

™ legal status of the National Electrical Safety Code in any particular state or locality within a state, the 

(tt authority having jurisdiction should be contacted. 

^ The revision cycle for the 2007 edition of the NESC will be fully electronic. Change proposals and 

■ comments will no longer be accepted in hard copy, but will be submitted to the NESC Secretary online via 

V the Internet. For information on how this electronic revision process will take place and for updates and 

g| complete information on the NESC, please visit the National Electrical Safety Code Zone on the IEEE 

Standards Web site at http://standardsJeee.org/nesc. 



I 



v 
Copyright © 2001 IEEE. All rights reserved. 



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Copyright © 2001 IEEE. All rights reserved. 



Standards Committee Membership 

At the time this Code was approved, Accredited Standards Committee C2 had the following membership: 

O. Chuck Amrhyn, Chair Frank A. Denbrock, Vice Chair 
Susan L. Vogel, Secretary 

Organization Represented Name 

Alliance for Telephone Industry Solutions Lawrence M. Slavin 

American Insurance Services Group, Inc Vacant 

American Public Power Association Michael J. Hyland 

Ron Lunt (Alt.) 

American Public Transit Association George S. Pristach 

Association of American Railroads Vacant 

Association of Edison Illuminating Companies John J. Schlee, Jr. 

Bonneville Power Administration, US Department of Energy Jerry L. Reding 

Edison Electric Institute Stephen A. Olinick 

John W. Troglia (Alt.) 

David G. Komassa (Alt.) 

Electronic Industries Association Percy E. Pool 

Institute of Electrical and Electronics Engineers, Inc Frank A. Denbrock 

Jerome G. Hanson (Alt.) 

Vernon R. Lawson (Alt.) 

International Association of Government Labor Officials Bernard O'Neill 

International Brotherhood of Electrical Workers James R. Tomaseski 

International Municipal Signal Association Warren Farrell 

National Association of Regulatory Utility Commissioners B. J. Washburn 

National Cable Television Association F. N. Wilkenloh 

Rex Bullinger (Alt.) 
National Electrical Contractors Association O. L. Davis 

Brooke H. Stauffer (Alt.) 
National Electrical Manufacturers Association Chris K. Durland 

Lawrence F. Miller (Alt.) 

National Safety Council P. Schmidt 

National Society of Professional Engineers William F. Fuller 

Rural Utilities Service, US Department of Agriculture G. J. Bagnall 

Tennessee Valley Authority Clayton L. Clem 

Nancy A. Knowles (Alt.) 

Western Area Power Administration, US Department of Energy Oliver W. Perkins 

Individual Member . v O. Chuck Amrhyn 

Individual Member Allen L. Clapp 

Liaison Representative to Canadian Electrical Code Susan L. Vogel 

Canadian Standards Association Liaison Representative David Singleton 



vn 
Copyright © 2001 IEEE. All rights reserved. 



I 



Subcommittee 1 

Purpose, Scope, Application, Definitions, and References 

(Sections 1,2, and 3) 



Allen L. Clapp, Chair 



Charles C. Bleakley, Secretary 



O. Chuck Amrhyn 
Charles C. Bleakley 

David E. Bouchard 
Frank A. Denbrock 

Allen L. Clapp 
D. J. Christofersen 

Robert E. Sipler, Jr. 



(Main) 




JohnB.Dagenhart 


(SC2) 


(SC7) 




Donald E. Hooper 


(Interpretations) 


(Alt.) 




Ewell T. Robeson 


(Alt.) 


(SC5) 




Henry J. Kientz 


(SC8) 


(Alt.) 




James R. Tomaseski 


(Alt.) 


(SC3) 




David G. Komassa 


(SC4) 


(Alt.) 




Eric K. Engdahl 


{Alt) 


Subcommittee 2 




Grounding Methods 






(Section 9) 







John B. Dagenhart, Chair 

J. Boksiner 
Harvey L. Bowles 
A. C. Channaiah 

Terry Page 
JohnB.Dagenhart 
M. M. Dixon 

L. E. Gaunt 

William J. Turner 



Ewell T. Robeson, Secretary 



D. J. Christofersen, Chair 

D. J. Christofersen 
A. L. Comans 
W. Bruce Dietzman 
Gary R. Engmann 
C. C. Hamerla 
S.J. Kollmann 
Brian Winoski 



ATIS 


N. Maxwell 


NARUC 


RUS 


Robert Molde 


EEI 


SEEX 


Michael A. Moore 


APPA 


(Alt.) 


Percy E. Pool 


EIA 


IEEE 


Ewell T. Robeson 


EEI 


EEI 


James R. Tomaseski 


IBEW 


(Alt.) 


Donald W.Zipse 


IEEE 


(Alt.) 






Subcommittee 3 




Electric Supply Stations 




(Sections 10-19) 






Robert E. Sipler, Jr. 


, Secretary 


IEEE 


N. Burch Lewis 


SEEX 


AEIC 


K. C. Labbe 


(Alt.) 


IEEE 


Thomas McNamara 


NEMA 


IEEE 


Robert E. Sipler, Jr. 


NARUC 


EEI 


James R. Tomaseski 


IBEW 


EEI 


Philip Young 


EEI 


(Alt.) 


George Zaczek 


APPA 



AAR — Association of American Railroads 

AEIC— Association of Edison Illuminating Companies 

AISG— American Insurance Services Group, Inc. 

AISI— American Iron and Steel Institute 

APPA— American Public Power Association 

APT A— American Public Transit Association 

ATIS— Alliance for Telephone Industry Solutions 

AWPA— American Wood Preserves Assocation 

BPA— Bonneville Power Admin., US Dept. of Energy 

EEI— Edison Electric Institute 

EIA — Electronic Industries Association 

IAGLO— Int'l. Assoc, of Government Labor Officials 



IBEW— International Brotherhood of Electrical Workers 

IEEE— Institute of Electrical and Electronics Engineers, Inc. 

IMSA— International Municipal Signal Association 

NARUC— National Association of Regulatory Utility Commissioners 

NCTA— National Cable Television Association 

NECA— National Electrical Contractors Association 

NEMA— National Electrical Manufacturers Association 

NSC— National Safety Council 

NSPE— National Society of Professional Engineers 

RUS — Rural Utilities Services , US Dept. of Agriculture 

SEEX— Southeastern Electric Exchange 

TVA— Tennessee Valley Authority 

WAPA— Western Area Power Administration, US Dept. of Energy 



Vlll 



Copyright © 2001 IEEE. All rights reserved. 



David G. Komassa, Chair 



Subcommittee 4 
Overhead Lines— Clearances 

(Section 20, 21,22, and 23) 



Eric K. Engdahl, Secretary 



I 



O. Chuck Amrhyn 
R. J. Bednarz 
Charles C. Bleakley 
James. L. Bohlk 
Allen L. Clapp 
Charles Crawford 
Thomas R. Crowell 

Phillip S.Givens 
Darrell D. Davidchik 
Eric K. Engdahl 

Kevin Drzewiecki 
Mickey B.Gunter 
Dennis Henry 
Donald E. Hooper 
Jan Howard 



Self 


H.N. Johnson, Jr. 


Self 


D. C. Young 


AEIC 


David G. Komassa 


RUS 


Stephen A. Olinick 


Self 


Robert G. Oswald 


NSPE 


Oliver W. Perkins 


EEI 


Jerry L. Reding 


(Alt.) 


Joseph Renowden 


EIA 


James Ruehl 


EEI 


Mathew C. Schwarz 


(Alt.) 


Lawrence M. Slavin 


EEI 


R. H. Stevens 


ATIS 


James R. Tomaseski 


Self 


B.J.Washburn 


APPA 


F. N. Wilkenloh 



SEEX 

(Alt.) 

EEI 

EEI 

IEEE 

WAPA 

BPA 

Emeritus 

NARUC 

IEEE 

ATIS 

Self 

IBEW 

NARUC 

NCTA 



Subcommittee 5 
Overhead Lines— Strength and Loading 

(Sections 24, 25, 26, and 27) 



Frank A. Denbrock, Chair 



Allen L. Clapp, Secretary 



Julian Ajello 


NARUC 


Leon Kempner, Jr. 


Nelson G. Bingel 


AWPA 


Robert O. Kluge 


Allen L. Clapp 


Self 


Michael Madore 


Clayton L. Clem 


TVA 


Robert C. Peters 


Darrell. D. Davidchik 


EIA 


T. A. Pinkham 


Frank A. Denbrock 


IEEE 


Joseph Rempe 


Nicholas J. DeSantis 


EEI 


Andrew Schwalm 


Thomas Diamantis 


(Alt.) 


E. Wade Shultz 


Bruce Freimark 


EEI 


R. Corzine 


William. F. Fuller 


NSPE 


Camille G. Rubeiz 


Douglas Hanson 


WAPA 


Brian Lacoursiere 


Jerome G. Hanson 


Self 


Richard Aichinger 


Edward Harrel 


EEI 


Lawrence M. Slavin 


Donald G. Heald 


RUS 


Richard J. Standford 


Richard W. Hensel 


IEEE 


Jerry C. Wong 


Walter D.Jones 


IEEE 





BPA 

EEI 

APPA 

IEEE 

IEEE 

EEI 

(Alt.) 

SEEX 

(Alt.) 

AISI 

(Alt.) 

(Alt.) 

ATIS 

EEI 

EEI 



IX 



Copyright © 2001 IEEE. All rights reserved. 



Charles C. Bleakley, Chair 



Subcommittee 7 

Underground Lines 

(Sections 30-39) 



David E. Bouchard, Secretary 
F. William Koch, Secretary (1987-2000) 



O. Chuck Amrhyn 
Charles C. Bleakley 

Mickey B.Gunter 
David E. Bouchard 
L. G. Clemons 

Donna L. Chaffin 
R. A. Fernandez 
Dennis Henry 
Trung Hiu 
David H. Kendall 



Self 

SEEX 

(Alt.) 

IEEE 

EEI 
(Alt.) 

EIA 

ATIS 

RUS 

NEMA 



James D. Mars 
Dennis B.Miller 
George S.Pristach 
Ewell T. Robeson 
Les Shankland 
Lawrence M. Slavin 
John C. Spence 
Monte Szendre 
James R. Tomaseski 
F. N. Wilkenloh 



Self 

EEI 

APTA 

IEEE 

APPA 

ATIS 

EEI 

NECA 

IBEW 

NCTA 



Henry J. Kientz, Chair 

George V. Causer 
J. M. Degen 
J. F. Doering 
C. W. Grose 
J. A. Dahmer 

Maury Dunn 
Robert A. Fass 

James Spadafore 
Dennis Henry 
Stephen L. Keys 

James C. Tuggle 

Robert W. Baird 
Henry J. Kientz 



Subcommittee 8 

Work Rules 
(Sections 40-44) 



WAPA 

ATIS 

Self 

Emeritus 

EEI 

(Alt) 

EEI 

(Alt.) 

ATIS 

mc 

(Alt.) 

(Alt.) 

Emeritus 



James R. Tomaseski, Secretary 



J. D. Mitchell 


IEEE 


Thomas Verdecchio 


(Alt.) 


R. C. Mooney 


AIEC 


Stephen Poholski 


NECA 


Thomas Ryder 


EIA 


Lawrence Schweitzer 


IEEE 


Les Shankland 


APPA 


R. D. Shores 


EIA 


Steven Theis 


NUCA 


James R. Tomaseski 


IBEW 


G. Tootle 


SEEX 


D. M. Wallis 


OSHA 


J. E. Pipkin 


(Alt.) 



Executive Subcommittee 



O. Chuck Amrhyn, Chair 

O. Chuck Amrhyn 
Frank A. Denbrock 
Michael J. Hyland 
Stephen A. Olinick 



Frank A. Denbrock, Vice Chair 



Self 

IEEE 

APPA 

EEI 



Lawrence M. Slavin 
B.J.Washburn 
James R. Tomaseski 



ATIS 

NARUC 

IBEW 



Noelle D. Humenick 
IEEE Standards Project Editor 



Copyright © 2001 IEEE. All rights reserved. 



Contents 



SECTION PAGE 

Letter Symbols for Units xxxiii 

Sec. 1 . Introduction to the National Electrical Safety Code 

010. Purpose 

Oil. Scope 

012. General Rules 

013. Application 

A. New Installations and Extensions 

B. Existing Installations 2 

014. Waiver 2 

A. Emergency Installations 2 

B. Temporary Overhead Installations 2 

015. Intent 2 

016. Effective Date 3 

017. Units of Measure 3 



I 



Sec. 2. Definitions of Special Terms '. 4 

Sec. 3. References 14 

Sec . 9 . Grounding Methods for Electric Supply and Communications Facilities 16 

90. Purpose 16 

91. Scope 16 

92. Point of Connection of Grounding Conductor 16 

A. Direct Current Systems That Are to Be Grounded 16 

1. 750 V and below 16 

2. Over 750 V 16 

B. Alternating Current Systems That Are to Be Grounded 16 

1. 750 V and below ; 16 

2. Over 750 V 16 

3. Separate Grounding Conductor 17 

C. Messenger Wires and Guys 17 

1. Messenger Wires 17 

2. Guys 17 

3. Common Grounding of Messengers and Guys on the Same 

Supporting Structure 17 

D. Current in Grounding Conductor 17 

E. Fences 18 

93. Grounding Conductor and Means of Connection 18 

A. Composition of Grounding Conductors 18 

B. Connection of Grounding Conductors 19 

C. Ampacity and Strength 19 

1 . System Grounding Conductors for Single-Grounded Systems 19 

2. System Grounding Conductors for Multi-Grounded Alternating 

Current Systems 19 

3. Grounding Conductors for Instrument Transformers 19 

4. Grounding Conductors for Primary Surge Arresters 19 

5. Grounding Conductors for Equipment, Messenger Wires, and Guys 19 

6. Fences 19 

7. Bonding of Equipment Frames and Enclosures 20 

8. Ampacity Limit 20 

xi 
Copyright © 2001 IEEE. All rights reserved. 



Contents 

SECTION PAGE 
9. Strength 20 

D. Guarding and Protection 20 

E. Underground 20 

F. Common Grounding Conductor for Circuits, Metal Raceways, and 

Equipment 21 

94. Grounding Electrodes 21 

A. Existing Electrodes 21 

1. Metallic Water Piping System 21 

2. Local Systems 21 

3. Steel Reinforcing Bars in Concrete Foundations and Footings 21 

B. Made Electrodes 21 

1. General 21 

2. Driven Rods 22 

3. Buried Wire, Strips, or Plates 22 

4. Pole-Butt Plates and Wire Wraps 22 

5. Concentric Neutral Cable 23 

6. Concrete-Encased Electrodes 23 

95. Method of Connection to Electrode 23 

A. Ground Connections 23 

B. Point of Connection to Piping Systems 24 

C. Contact Surfaces 24 

96. Ground Resistance Requirements 24 

A. Supply Stations 24 

B. Single-Grounded (Unigrounded or Delta) Systems 24 

C. Multi-Grounded Systems 24 

97. Separation of Grounding Conductors 25 

98. Number 98 not used in this edition 26 

99. Additional Requirements for Communication Apparatus 26 

A. Electrode 26 

B. Electrode Connection 26 

C. Bonding of Electrodes 26 

Part 1. Rules for the Installation and Maintenance of Electric Supply Stations and 
Equipment 

Sec. 10. Purpose and Scope of Rules 27 

100. Purpose 27 

101. Scope 27 

Sec. 11. Protective Arrangements in Electric Supply Stations 28 

110. General Requirements 28 

A. Enclosure of Equipment 28 

1. Types of Enclosures 28 

2. Safety Clearance Zone 28 

B. Rooms' and Spaces 28 

1. Construction 28 

2. Use 28 

3. Ventilation 30 

4. Moisture and Weather 30 

C. Electric Equipment 30 

111. Illumination 30 

A. Under Normal Conditions 30 

B. Emergency Lighting 30 

C. Fixtures 30 

D. Attachment Plugs and Receptacles for General Use 30 

xii 
Copyright © 2001 IEEE. All rights reserved. 



Contents 

SECTION PAGE 

E. Receptacles in Damp or Wet Locations 30 

112. Floors, Floor Openings, Passageways, and Stairs 32 

A. Floors 32 

B. Passageways 32 

C. Railings 33 

D. Stair Guards 33 

E. Top Rails 33 

113. Exits 33 

A. Clear Exits 33 

B. Double Exits 33 

C. Exit Doors 33 

1 14. Fire-Extinguishing Equipment 33 

Sec. 12. Installation and Maintenance of Equipment 34 

120. General Requirements 34 

121. Inspections 34 

A. In-Service Equipment 34 

B. Idle Equipment 34 

C. Emergency Equipment 34 

D. New Equipment 34 

122. Guarding Shaft Ends, Pulleys, Belts, and Suddenly Moving Parts 34 

A. Mechanical Transmission Machinery 34 

B. Suddenly Moving Parts 34 

123. Protective Grounding 34 

A. Protective Grounding or Physical Isolation of Non-Current-Carrying 

Metal Parts 34 

B. Grounding Method 34 

C. Provision for Grounding Equipment During Maintenance 35 

D. Grounding Methods for Direct-Current Systems over 750 V 35 

124. Guarding Live Parts 35 

A. Where Required 35 

B. Strength of Guards 35 

C. Types of Guards 35 

1. Location or Physical Isolation 35 

2. Shields or Enclosures 35 

3. Supplemental Barriers or Guards Within Electric Supply Stations 36 

4. Mats 36 

5. Live Parts Below Supporting Surfaces for Persons 36 

6. Insulating Covering on Conductors or Parts 36 

125. Working Space About Electric Equipment 45 

A. Working Space (600 V or Less) 45 

1. Clear Spaces 45 

2. Access and Entrance to Working Space 45 

3. Working Space 45 

4. Headroom Working Space 45 

5. Front Working Space 45 

B. Working Space Over 600 V 45 

126. Equipment for Work on Energized Parts 46 

127. Classified Locations 46 

A. Coal-Handling Areas 46 

B. Flammable and Combustible Liquids 46 

C. Flammable Liquid Storage Area 47 

D. Loading and Unloading Facilities 47 



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Contents 

SECTION PAGE 

E. Gasoline-Dispensing Stations 47 

F. Boilers 47 

G. Gaseous Hydrogen Systems for Supply Equipment 47 

H. Liquid Hydrogen Systems 48 

J 5 I- Sulfur 48 

^ $ J. Oxygen 48 

K. Liquefied Petroleum Gas (LPG) 48 

L. Natural Gas (Methane) 48 

128. Identification 48 

129. Mobile Hydrogen Equipment 48 

Sec. 13. Rotating Equipment 49 

130. Speed Control and Stopping Devices 49 

A. Automatic Overspeed Trip Device for Prime Movers 49 

B. Manual Stopping Devices 49 

C. Speed Limit for Motors 49 

D. Number 130D not used in this edition 49 

E. Adjustable-Speed Motors 49 

F. Protection of Control Circuits 49 

131. Motor Control 49 

132. Number 132 not used in this edition 49 

133. Short-Circuit Protection 49 

Sec. 14. Storage Batteries 50 

140. General 50 

141. Location 50 

142. Ventilation 50 

143. Racks 50 

144. Floors in Battery Areas 50 

145. Illumination for Battery Areas 50 

146. Service Facilities 50 

147. Number 147 not used in this edition 50 

Sec. 15. Transformers and Regulators 51 

150. Current-Transformer Secondary Circuits Protection When Exceeding 

600 V 51 

151. Grounding Secondary Circuits of Instrument Transformers 51 

152. Location and Arrangement of Power Transformers and Regulators 51 

A. Outdoor Installations 51 

B. Indoor Installations 51 

153. Short-Circuit Protection of Power Transformers 51 

Sec. 16. Conductors 53 

160. Application 53 

161. Electrical Protection 53 

A. Overcurrent Protection Required 53 

B. Grounded Conductors 53 

C. Insulated Power Cables 53 

162. Mechanical Protection and Support 53 

163. Isolation 53 

164. Conductor Terminations 53 

A. Insulation 53 

B. Metal-Sheathed or Shielded Cable 53 

Sec. 17. Circuit Breakers, Reclosers, Switches, and Fuses 54 

170. Arrangement 54 

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Contents 

SECTION PAGE 

171. Application 54 

172. Circuit Breakers, Reclosers, and Switches Containing Oil 54 

173. Switches and Disconnecting Devices 54 

A. Capacity 54 

B. Provisions for Disconnecting 54 

C. Visible Break Switch 54 

174. Disconnection of Fuses 54 

Sec. 18. Switchgear and Metal-Enclosed Bus 55 

180. Switchgear Assemblies 55 

A. General Requirements for All Switchgear 55 

B. Metal-Enclosed Power Switchgear 55 

C. Dead-Front Power Switchboards 56 

D. Motor Control Centers 56 

E. Control Switchboards ; 56 

181. Metal-Enclosed Bus 56 

A. General Requirements for All Types of Bus 56 

B. Isolated-Phase Bus 56 

Sec. 19. Surge Arresters 58 

190. General Requirements 58 

191. Indoor Locations 58 

192. Grounding Conductors 58 

193. Installation 58 

Part 2. Safety Rules for the Installation and Maintenance of Overhead 
Electric Supply and Communication Lines 

Sec. 20. Purpose, Scope, and Application of Rules 59 

200. Purpose 59 

201. Scope 59 

202. Application of Rules 59 

Sec. 21. General Requirements 60 

210. Referenced Sections 60 

211. Number 211 not used in this edition 60 

212. Induced Voltages 60 

213. Accessibility 60 

214. Inspection and Tests of Lines and Equipment 60 

A. When In Service 60 

1 . Initial Compliance With Rules 60 

2. Inspection 60 

3. Tests 60 

4. Record of Defects 60 

5. Remedying Defects 60 

B. When Out of Service 60 

1. Lines Infrequently Used 60 

2. Lines Temporarily Out of Service 60 

3. Lines Permanently Abandoned 60 

215. Grounding of Circuits, Supporting Structures, and Equipment 61 

A. Methods 61 

B. Circuits 61 

1. Common Neutral 61 

2. Other Neutrals 61 

3. Other Conductors 61 

4. Surge Arresters 61 

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Contents 
SECTION PAGE 

5. Use of Earth as Part of Circuit 61 

C. Non-Current-Carrying Parts 61 

1. General 61 

*.* 2. Guys 61 

felljh 3. Multiple Messengers on the Same Structure 61 

p&j 216. Arrangement of Switches 62 

A. Accessibility 62 

B. Indicating Open or Closed Position 62 

C. Locking 62 

D. Uniform Position 62 

217. General 62 

A. Supporting Structures 62 

1. Protection of Structures 62 

2. Readily Climbable Supporting Structures 62 

3. Identification 63 

4. Obstructions 63 

5. Decorative Lighting 63 

B. Unusual Conductor Supports 63 

218. Tree Trimming 63 

A. General 63 

B. At Line Crossings, Railroad Crossings, and Limited- Access 

Highway Crossings 63 

Sec. 22. Relations Between Various Classes of Lines and Equipment 64 

220. Relative Levels 64 

A. Standardization of Levels 64 

B. Relative Levels: Supply and Communication Conductors 64 

1. Preferred Levels 64 

2 . Special Construction for Supply Circuits , the Voltage of Which Is 

600 V or Less and Carrying Power Not in Excess of 5 kW 64 

C. Relative Levels: Supply Lines of Different Voltage Classifications 

(as classified in Table 235-5) 65 

1. At Crossings or Conflicts 65 

2. On Structures Used Only by Supply Conductors 65 

D. Identification of Overhead Conductors 65 

E. Identification of Equipment on Supporting Structures 65 

221. Avoidance of Conflict 65 

222. Joint Use of Structures 65 

223. Communications Protective Requirements 66 

A. Where Required 66 

B. Means of Protection 66 

224. Communication Circuits Located Within the Supply Space and 

Supply Circuits Located Within the Communication Space 66 

A. Communication Circuits Located in the Supply Space 66 

B . Supply Circuits Used Exclusively in the Operation of Communication Circuits 67 

225. Electric Railway Construction 67 

A. Trolley-Contact Conductor Fastenings 67 

B. High- Voltage Contact Conductors 67 

C. Third Rails 67 

D. Prevention of Loss of Contact at Railroad Crossings at Grade 67 

E. Guards Under Bridges 68 

Sec. 23. Clearances 69 

230. General 69 

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A. Application 69 

1 . Permanent and Temporary Installations 69 

2. Emergency Installations 69 

B. Measurement of Clearance and Spacing 69 

C. Supply Cables 69 

D. Covered Conductors 70 

E. Neutral Conductors 70 

F. Fiber-Optic Cable 70 

1. Fiber-optic— supply cable 70 

2. Fiber-optic— communication cable 70 

G. Alternating- and Direct-Current Circuits 70 

H. Constant-Current Circuits 70 

I. Maintenance of Clearances andSpacings 71 

231. Clearances of Supporting Structures From Other Objects 71 

A. From Fire Hydrants 71 

B. From Streets, Roads, and Highways 71 

C. From Railroad Tracks 71 

232. Vertical Clearances of Wires, Conductors, Cables, and Equipment Above 

Ground, Roadway, Rail, or Water Surfaces 71 

A. Application 71 

B . Clearance of Wires , Conductors , Cables , Equipment , and Support Arms 

Mounted on Supporting Structures 72 

1. Clearance to Wires, Conductors, and Cables 72 

2. Clearance to Unguarded Rigid Live Parts of Equipment 72 

3. Clearance to Support Arms and Equipment Cases 72 

4. Street and Area Lighting 72 

C . Additional Clearances for Wires , Conductors , Cables , and Unguarded 

Rigid Live Parts of Equipment 72 

1. Voltages Exceeding 22 kV 72 

D. Alternate Clearances for Voltages Exceeding 98 kV AC to Ground 

or 139 kV DC to Ground 73 

1. Sag Conditions of Line Conductors 73 

2. Reference Heights 73 

3. Electrical Component of Clearance 73 

4. Limit 73 

233. Clearances Between Wires, Conductors, and Cables Carried on Different 

Supporting Structures 85 

A. General 85 

1. Conductor Movement Envelope 85 

2. Clearance Envelope 85 

B. Horizontal Clearance 89 

1. Clearance Requirements 89 

2. Alternate Clearances for Voltages Exceeding 98 kV AC to Ground 

or 139 kV DC to Ground 89 

C. Vertical Clearance 89 

1. Clearance Requirements 89 

2. Voltages Exceeding 22 kV 89 

3. Alternate Clearances for Voltage Exceeding 98 kV AC to Ground 

or 139 kV DC to Ground 90 

234. Clearance of Wires, Conductors, Cables, and Equipment From Buildings, 

Bridges, Rail Cars, Swimming Pools, and Other Installations 96 

A. Application 96 

1 . Vertical and Horizontal Clearances (No Wind Displacement) 96 

2. Horizontal Clearances (With Wind Displacement) 96 

xvii 
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SECTION PAGE 
3. Transition Between Horizontal and Vertical Clearances 96 

B . Clearances of Wires , Conductors , and Cables From Other Supporting 

Structures 96 

C . Clearances of Wires , Conductors , Cables , and Rigid Live Parts 
From Buildings, Signs, Billboards, Chimneys, Radio and Television 

Antennas, Tanks, and Other Installations Except Bridges 99 

1 . Vertical and Horizontal Clearances 99 

2. Guarding of Supply Conductors and Rigid Live Parts 99 

3 . Supply Conductors Attached to Buildings or Other Installations 99 

4. Communication Conductors Attached to Buildings or Other 

Installations 100 

5. Ladder Space 100 

D. Clearance of Wires, Conductors, Cables, and Unguarded Rigid Live Parts 

From Bridges 107 

1. Vertical and Horizontal Clearances 107 

2. Guarding Trolley-Contact Conductors Located Under Bridges 109 

E. Clearance of Wires, Conductors, Cables, or Unguarded Rigid Live Parts 

Installed Over or Near Swimming Areas With No Wind Displacement 109 

1. Swimming Pools 109 

2. Beaches and Waterways Restricted to Swimming 109 

3. Waterways Subject to Water Skiing 109 

F. Clearances of Wires, Conductors, Cables, and Rigid Live Parts 

From Grain Bins 114 

1 . Grain Bins Loaded by Permanently Installed Augers, Conveyers, 

or Elevator Systems 114 

2. Grain Bins Loaded by Portable Augers, Conveyers or Elevators 

(With No Wind Displacement) 115 

G. Additional Clearances for Voltages Exceeding 22 kV for Wires, 

Conductors , Cables , and Unguarded Rigid Live Parts of Equipment 117 

H. Alternate Clearances for Voltages Exceeding 98 kV AC to Ground 

or 139 kV DC to Ground 117 

1. Sag Conditions of Line Conductors 117 

2. Reference Distances 117 

3. Electrical Component of Clearance 117 

4. Limit 118 

I. Clearance of Wires, Conductors, and Cables to Rail Cars 118 

1. Rules 232B1 and232Cl 118 

2. Rule232D 118 

J. Clearance of Equipment Mounted on Supporting Structures 118 

1. Clearance to Unguarded Rigid Live Parts of Equipment 118 

2. Clearance to Equipment Cases 118 

235 . Clearance for Wires, Conductors, or Cables Carried on the Same Supporting 

Structure 121 

A. Application of Rule 121 

1 . Multiconductor Wires or Cables 121 

2. Conductors Supported by Messengers or Span Wires 121 

3. Line Conductors of Different Circuits 121 

B. Horizontal Clearance Between Line Conductors 121 

1. Fixed Supports 121 

2. Suspension Insulators 126 

3. Alternate Clearances for Different Circuits Where One or Both 

Circuits Exceed 98 kV AC to Ground or 139 kV DC to Ground 126 

C. Vertical Clearance Between Line Conductors 126 

1. Basic Clearance for Conductors of Same or Different Circuits 127 

xviii 
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Contents 

SECTION PAGE 

2. Additional Clearances 127 

3. Alternate Clearances for Different Circuits Where One or Both 

Exceed 98 kV AC, or 139 kV DC to Ground 133 

4. Communication Worker Safety Zone 133 

D. Diagonal Clearance Between Line Wires, Conductors, and Cables 

Located at Different Levels on the Same Supporting Structure 134 

E. Clearances in Any Direction From Line Conductors to Supports, 
and to Vertical or Lateral Conductors, Span, or Guy Wires Attached 

to the Same Support 138 

1. Fixed Supports 138 

2. Suspension Insulators 138 

3. Alternate Clearances for Voltages Exceeding 98 kV AC to Ground 

or 139 kV DC to Ground 138 

F. Clearances Between Circuits of Different Voltage Classifications 

Located in the Supply Space on the Same Support Arm 139 

G. Conductor Spacing: Vertical Racks 140 

H. Clearance and Spacing Between Communication Conductors, 

Cables, and Equipment 141 

I. Clearances in Any Direction From Supply Line Conductors to 

Communication Antennas in the Supply Space Attached to the Same 

Supporting Structure 141 

236. Climbing Space 141 

A. Location and Dimensions 141 

B. Portions of Supporting Structures in Climbing Space 141 

C. Support Arm Location Relative to Climbing Space 142 

D. Location of Equipment Relative to Climbing Space 142 

E. Climbing Space Between Conductors 142 

F. Climbing Space on Buckarm Construction 144 

G. Climbing Space Past Longitudinal Runs Not on Support Arms 144 

H. Climbing Space Past Vertical Conductors 144 

I. Climbing Space Near Ridge-Pin Conductors 144 

237. Working Space 145 

A. Location of Working Spaces 145 

B. Dimensions of Working Spaces 145 

1. Along the Support Arm 145 

2. At Right Angles to the Support Arm 145 

3. Vertically 145 

C. Location of Vertical and Lateral Conductors Relative to Working 

Spaces 146 

D. Location of Buckarms Relative to Working Spaces 146 

1. Standard Height of Working Space 146 

2. Reduced Height of Working Space 146 

E. Guarding of Energized Equipment 146 

F. Working Clearances From Energized Equipment 146 

238. Vertical Clearance Between Certain Communications and Supply Facilities 

Located on the Same Structure 147 

A. Equipment 147 

B. Clearances in General 147 

C. Clearances for Span Wires or Brackets 147 

D. Clearance of Drip Loops of Luminaire or Traffic Signal Brackets 147 

E. Communication Worker Safety Zone 147 

239. Clearance of Vertical and Lateral Facilities From Other Facilities and 

Surfaces on the Same Supporting Structure 149 

A. General 149 

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Contents 

SECTION PAGE 

B . Location of Vertical or Lateral Conductors Relative to Climbing 

Spaces, Working Spaces, and Pole Steps 149 

C. Conductors Not in Conduit 149 

^ffjlj D. Guarding and Protection Near Ground 149 

*' *fc E. Requirements for Vertical and Lateral Supply Conductors on Supply 

Line Structures or Within Supply Space on Jointly Used Structures 149 

1. General Clearances 149 

2. Special Cases 149 

F. Requirements for Vertical and Lateral Communication Conductors 
on Communication Line Structures or Within the Communication 
Space on Jointly Used Structures 150 

1 . Clearances From Communication Conductors 150 

2. Clearances From Supporting Structure Surfaces 150 

G. Requirements for Vertical Supply Conductors and Cables Passing Through 
Communication Space on Jointly Used Line Structures '. 150 

1. Guarding— General 150 

2. Cables and Conductors in Conduit or Covering 151 

3. Protection Near Trolley, Ungrounded Traffic Signal, or 
Ungrounded Luminaire Attachments 151 

4. Aerial Services 151 

5. Clearance From Through Bolts and Other Metal Objects 151 

H. Requirements for Vertical Communication Conductors Passing 

Through Supply Space on Jointly Used Structures 151 

1. Metal-Sheathed Communication Cables 151 

2. Communication Conductors 151 

3. Communication Grounding Conductors 151 

4. Clearance From Through Bolts and Other Metal Objects 152 

I. Operating Rods 152 

J. Additional Rules for Standoff Brackets 152 

Sec. 24 Grades of Construction 155 

240. General 155 

241. Application of Grades of Construction to Different Situations 155 

A. Supply Cables 155 

B. Order of Grades 155 

C. At Crossings 155 

1. Grade of Upper Line 155 

2. Grade of Lower Line 155 

3. Multiple Crossings 155 

D. Conflicts 155 

242. Grades of Construction for Conductors 155 

A. Constant-Current Circuit Conductors 156 

B. Railway Feeder and Trolley-Contact Circuit Conductors 156 

C. Communication Circuit Conductors Located in the Supply Space 156 

D. Fire- Alarm Circuit Conductors 156 

E. Neutral Conductors of Supply Circuits 156 

F. Surge-Protection Wires 156 

243. Grades of Construction for Line Supports 160 

A. Structures 160 

B. Crossarms and Support Arms 160 

C . Pins , Armless Construction Brackets , Insulators , and 
Conductor Fastenings 160 

Sec. 25. Loading for Grades B andC 161 

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Contents 

SECTION PAGE 

250. General Loading Requirements and Maps 161 

A. General 161 

B. Combined Ice and Wind Loading 161 

C. Extreme Wind Loading 161 

1. Velocity Pressure Exposure Coefficient k z 163 

2. Gust Response Factor, Grj? 163 

251. Conductor Loading 170 

A. General 170 

B. Load Components 170 

1. Vertical Load Component 170 

2. Horizontal Load Component 170 

3. Total Load 170 

252. Loads on Line Supports 171 

A. Assumed Vertical Loads 171 

B. Assumed Transverse Loads 171 

1. Transverse Loads From Conductors and Messengers 171 

2. Wind Loads on Structures 171 

3. At Angles 171 

4. Span Lengths 171 

C. Assumed Longitudinal Loading 171 

1. Change in Grade of Construction 171 

2. Jointly Used Poles at Crossings Over Railroads, Communication 

Lines, or Limited-Access Highways 172 

3. Deadends 172 

4. Unequal Spans and Unequal Vertical Loads 172 

5. Stringing Loads 172 

6. Longitudinal Capability 172 

7. Communication Conductors on Unguyed Supports at Railroad 

and Limited-Access Highway Crossings 172 

D. Simultaneous Application of Loads 172 

253. Overload Factors for Structures, Crossarms, Support Hardware, Guys, 

Foundations, and Anchors 172 

Sec. 26. Strength Requirements 175 

260. General (see also Section 20) 175 

A. Preliminary Assumptions 175 

B. Application of Strength Factors 175 

261 . Grades B and C Construction 175 

A. Supporting Structures 175 

1. Metal, Prestressed-, and Reinforced-Concrete Structures 175 

2. Wood Structures 176 

3. Transverse-Strength Requirements for Structures Where Side 

Guying Is Required, But Can Only Be Installed at a Distance 177 

4. Longitudinal-Strength Requirements for Sections of Higher Grade 

in Lines of a Lower-Grade Construction 177 

B. Strength of Foundations, Settings, and Guy Anchors 177 

C. Strength of Guys and Guy Insulators 177 

1. Metal and Prestressed-Concrete Structures 177 

2. Wood and Reinforced-Concrete Poles and Structures 177 

D. Crossarms and Braces 178 

1 . Concrete and Metal Crossarms and Braces 178 

2. Wood Crossarms and Braces 178 

3. Crossarms and Braces of Other Materials 178 

4. Additional Requirements 178 

xxi 
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Contents 

SECTION PAGE 

E. Insulators 179 

F. Strength of Pin-Type or Similar Construction and Conductor 

Fastenings 179 

1. Longitudinal Strength 179 

2. Double Pins and Conductor Fastenings 179 

3. Single Supports Used in Lieu of Double Wood Pins 179 

G. Armless Construction 179 

1. General 179 

2. Insulating Material 179 

3. Other Components 179 

H. Open Supply Conductors and Overhead Shield Wires 179 

1. Sags and Tensions 179 

2. Splices, Taps, and Dead-End Fittings 180 

3. Trolley-Contact Conductors 180 

I. Supply Cable Messengers 180 

J. Open-Wire Communication Conductors 180 

K. Communication Cables 180 

L. Paired Communication Conductors 180 

1. Paired Conductors Supported on Messenger 180 

2. Paired Conductors Not Supported on Messenger 181 

M. Support Hardware 181 

262. Number 262 not used in this edition '. 183 

263. Grade N Construction 183 

A. Poles 183 

B. Guys 183 

C. Crossarm Strength 183 

D. Supply-Line Conductors 183 

E. Service Drops 183 

1. Size of Open- Wire Service Drops 183 

2. Tension of Open- Wire Service Drops 184 

3. Cabled Service Drops 184 

F. Trolley-Contact Conductors 184 

G. Communication Conductors 184 

H. Street and Area Lighting Equipment 184 

I. Insulators 184 

264. Guying and Bracing 185 

A. Where Used 185 

B. Strength 185 

C. Point of Attachment 185 

D. Guy Fastenings 185 

E. Guy Markers and Protection 186 

F. Electrolysis 186 

G. Anchor Rods 186 

Sec. 27. Line Insulation 187 

270. Application of Rule 187 

271. Material and Marking 187 

272. Ratio of Flashover to Puncture Voltage 187 

273. Insulation Level 187 

274. Factory Tests 187 

275. Special Insulator Applications : 187 

A. Insulators for Constant-Current Circuits 187 

B . Insulators for Single-Phase Circuits Directly Connected to 

Three-Phase Circuits 188 

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Contents 

SECTION PAGE 

276. Number 276 Not Used in this Edition 188 

277. Mechanical Strength of Insulators 188 

278. Aerial Cable Systems 188 

A. Electrical Requirements 188 

B. Mechanical Requirements 189 

279. Guy and Span Insulators 189 

A. Insulators 189 

1. Properties of Guy Insulators 189 

2. Use of Guy Insulators 189 

3. Corrosion Protection 189 

B. Span- Wire Insulators 189 

1. Properties of Span-Wire Insulators 189 

2. Use of Span-Wire Insulators 190 

Sec. 28 Section number 28 not used in this edition 190 

Sec. 29 Section number 29 not used in this edition 190 

Part 3. Safety Rules for the Installation and Maintenance of Underground 
Electric Supply and Communication Lines 

Sec. 30. Purpose, Scope, and Application of Rules 191 

300. Purpose 191 

301. Scope 191 

302. Application of Rules 191 

Sec. 31. General Requirements Applying to Underground Lines 192 

310. Referenced Sections 192 

311. Installation and Maintenance 192 

312. Accessibility 192 

313. Inspection and Tests of Lines and Equipment 192 

A. When In Service 192 

1. Initial Compliance With Safety Rules 192 

2. Inspection 192 

3. Tests 192 

4. Record of Defects 192 

5. Remedying Defects 192 

B. When Out of Service , 192 

1. Lines Infrequently Used 192 

2. Lines Temporarily Out of Service 192 

3. Lines Permanently Abandoned 192 

314. Grounding of Circuits and Equipment 192 

A. Methods 192 

B. Conductive Parts to Be Grounded 192 

C. Circuits 193 

1. Neutrals 193 

2. Other Conductors 193 

3. Surge Arresters 193 

4. Use of Earth as Part of Circuit 193 

315. Communications Protective Requirements 193 

A. Where Required 193 

B. Means of Protection 193 

316. Induced Voltage 193 

Sec. 32. Underground Conduit Systems 194 

320. Location 194 

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Contents 

SECTION PAGE 

A. Routing 194 

1. General 194 

2. Natural Hazards 194 

3. Highways and Streets 194 

4. Bridges and Tunnels 194 

5. Crossing Railroad Tracks 194 

6. Submarine Crossing 194 

B. Separation From Other Underground Installations 194 

1. General 194 

2 . Separations Between Supply and Communication Conduit Systems 1 95 

3. Sewers, Sanitary and Storm 195 

4. Water Lines 195 

5. Gas and Other Fuel Lines 195 

6. Steam Lines 195 

321. Excavation and Backfill 195 

A. Trench 195 

B. Quality of Backfill 195 

322. Ducts and Joints 195 

A. General 195 

B. Installation 196 

1. Restraint 196 

2. Joints 196 

3. Externally Coated Pipe 196 

4. Building Walls 196 

5. Bridges 196 

6. In Vicinity of Manholes 196 

323. Manholes, Handholes, and Vaults 196 

A. Strength 196 

B. Dimensions 198 

C. Manhole Access 198 

D. Covers 198 

E. Vault and Utility Tunnel Access 198 

F. Ladder Requirements 199 

G. Drainage 199 

H. Ventilation 199 

I. Mechanical Protection 199 

J. Identification 199 

Sec. 33. Supply Cable 200 

330. General 200 

331. Sheaths and Jackets 200 

332. Shielding 200 

A. General 200 

B. Material 200 

333. Cable Accessories and Joints 200 

Sec. 34. Cable in Underground Structures 201 

340. General 201 

341. Installation 201 

A. General 201 

B. Cable in Manholes and Vaults 201 

1. Supports 201 

2. Clearance 201 

3. Identification 202 

342. Grounding and Bonding 202 

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Contents 

SECTION PAGE 

343. Fireproofing 202 

344. Communication Cables Containing Special Supply Circuits 202 

Sec. 35. Direct-Buried Cable 204 

350. General 204 

351. Location and Routing 204 

A. General 204 

B. Natural Hazards 205 

C. Other Conditions 205 

1. Swimming Pools 205 

2. Buildings and Other Structures 205 

3. Railroad Tracks 205 

4. Highways and Streets 206 

5. Submarine Crossings 206 

352. Installation 206 

A. Trenching 206 

B. Plowing 206 

C. Boring , 206 

D. Depth of Burial 206 

353. Deliberate Separations— Equal to or Greater Than 300 mm (12 in) 

From Underground Structures or Other 207 

A. General 207 

B. Crossings 207 

C. Parallel Facilities 207 

D. Thermal Protection 207 

354. Random Separation— Separation Less Than 300 mm (12 in) 

From Underground Structures or Other Cables 207 

A. General 207 

B. Supply Cables or Conductors 207 

C. Communication Cables or Conductors 207 

D. Supply and Communication Cables or Conductors 208 

1. General 208 

2 . Grounded B are or Semiconducting Jacketed Neutral Supply Cables 208 

3. Insulating Jacketed Grounded Neutral Supply Cables 209 

4. Insulating Jacketed Grounded Neutral Supply Cables in 

Nonmetallic Duct 209 

E. Supply and Communication Cables or Conductors and 

Non-Metallic Water and Sewer Lines 209 

Sec. 36. Risers 210 

360. General 210 

361. Installation 210 

362. Pole Risers— Additional Requirements 210 

363. Pad-Mounted Installations 210 

Sec. 37. Supply Cable Terminations 211 

370. General 211 

371. Support at Terminations 211 

372. Identification 211 

373. Clearances in Enclosures or Vaults 211 

374. Grounding 211 

Sec. 38. Equipment 212 

380. General 212 

381. Design 212 

382. Location in Underground Structures 213 

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Copyright © 2001 IEEE. All rights reserved. 



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Contents 

SECTION PAGE 

383. Installation 213 

384. Grounding 213 

385. Identification 213 

j«l| Sec. 39. Installation in Tunnels 214 

390. General 214 

■■■ 391. Environment 214 

Part 4. Rules for the Operation of Electric Supply and Communications 
Lines and Equipment 

Sec. 40. Purpose and Scope 215 

400. Purpose 215 

401. Scope 215 

402. Referenced Sections 215 

Sec. 41. Supply and Communications Systems— Rules for Employers 216 

410. General Requirements 216 

A. General 216 

B. Emergency Procedures and First Aid Rules 216 

C. Responsibility 216 

411. Protective Methods and Devices 216 

A. Methods 216 

B. Devices and Equipment 217 

C. Inspection and Testing of Protective Devices 217 

D. Signs and Tags for Employee Safety 217 

E. Identification and Location 217 

F. Fall Protection 217 

Sec. 42. General Rules for Employees 218 

420. Personal General Precautions 218 

A. Rules and Emergency Methods 218 

B. Qualifications of Employees 218 

C. Safeguarding Oneself and Others 218 

D. Energized or Unknown Conditions 218 

E. Ungrounded Metal Parts 218 

F. Arcing Conditions 219 

G. Liquid-Cell Batteries 219 

H. Tools and Protective Equipment 219 

I. Clothing 219 

J. Ladders and Supports 219 

K. Fall Protection 219 

L. Fire Extinguishers 220 

M. Machines or Moving Parts 220 

N. Fuses 220 

O. Cable Reels 220 

P. Street and Area Lighting 221 

421. General Operating Routines 221 

A. Duties of a First-Level Supervisor or Person in Charge 221 

B. Area Protection 221 

1. Areas Accessible to Vehicular and Pedestrian Traffic 221 

2. Areas Accessible to Employees Only 221 

3. Locations With Crossed or Fallen Wires 221 

C. Escort 221 

422. Overhead Line Operating Procedures 222 

A. Setting, Moving, or Removing Poles In or Near Energized Electric 

Supply Lines 222 

B. Checking Structures Before Climbing 222 

xxvi 
Copyright © 2001 IEEE. All rights reserved. 



Contents 

SECTION PAGE 

C. Installing and Removing Wires or Cables 222 

423. Underground Line Operating Procedures 222 

A. Guarding Manhole and Street Openings 222 

B. Testing for Gas in Manholes and Unventilated Vaults 222 

C. Flames 223 

D. Excavation 223 

E. Identification 223 

F. Operation of Power-Driven Equipment 223 

Sec. 43. Additional Rules for Communications Employees 224 

430. General 224 

431. Approach to Energized Conductors or Parts 224 

432. Joint-Use Structures 224 

433. Attendant on Surface at Joint-Use Manhole 224 

434. Sheath Continuity 224 

Sec. 44. Additional Rules for Supply Employees 226 

440. General 226 

441 . Energized Conductors or Parts 226 

A. Minimum Approach Distance to Live Parts 226 

1. General 226 

2. Precautions for Approach— Voltages from 51 V to 300 V 226 

3. Precautions for Approach— Voltages from 301 V to 72.5 kV 226 

4. Transient Overvoltage Control Above 72.5 kV 227 

5. Altitude Correction 227 

6. Calculation of Approach Distances 227 

B. Additional Approach Requirements 235 

C. Live-Line Tool Clear Insulation Length 235 

1. Clear Live-Line Tool Length 235 

2. Live-Line Conductor Support Tool Length 235 

442. Switching Control Procedures 236 

A. Designated Person 236 

B. Specific Work 236 

C. Operations at Stations 236 

D. Re-energizing After Work 236 

E . Tagging Electric Supply Circuits Associated With Work Activities 236 

F. Restoration of Service After Automatic Trip 237 

G. Repeating Oral Messages 237 

443. Work on Energized Lines and Equipment 237 

A. General Requirements 237 

B. Requirement for Assisting Employee 238 

C. Opening and Closing Switches 238 

D. Working Position 238 

E. Protecting Employees by Switches and Disconnectors 238 

F. Making Connections 238 

G. Switchgear 238 

H. Current Transformer Secondaries 238 

I. Capacitors 239 

J. Gas-Insulated Equipment 239 

K. Attendant on Surface , 239 

L. Unintentional Grounds on Delta Circuits 239 

444. De-energizing Equipment or Lines to Protect Employees 239 

A. Application of Rule 239 

B. Employee's Request 239 

C. Operating Switches, Disconnectors, and Tagging 239 

D. Employee's Protective Grounds 240 

E. Proceeding With Work 240 

F. Reporting Clear— Transferring Responsibility 240 

xxvii 
Copyright © 2001 IEEE. All rights reserved. 



m 



Contents 



G. Removal of Tags 240 

H. Sequence of Re-energizing 240 

445. Protective Grounds 241 

A. Installing Grounds 241 

1 . Current-Carrying Capacity of Grounds 241 

2. Initial Connections 241 

3. Test for Voltage 241 

4. Completing Grounds 241 

B. Removing Grounds 241 

446. Live Work 241 

447 Protection Against Arcing and Other Damage While Installing 

and Maintaining Insulators and Conductors 242 



xx vm 
Copyright © 2001 IEEE. All rights reserved. 



Contents 



FIGURES 



RULE 



PAGE 



Figure D-l. 
Figure 110-1 
Figure 124-1. 
Figure 124-2. 
Figure 233-1. 



Figure 
Figure 
Figure 
Figure 
Figure 
Figure 
Figure 
Figure 



233-2. 
233-3. 
234-l(a) 
234- 1(b) 
234- 1(c) 
234-2. 
234-3. 
234-4(a) 



Figure 234-4(b) 

Figure 234-5 
Figure 235-1. 
Figure 236-1. 
Figure 237-1. 
Figure 250-1. 



Figure 
Figure 
Figure 
Figure 
Figure 
Figure 
Figure 
Figure 



250-2(a) 

250-2(b) 

250-2(c) 

250-2(d) 

250-2(e) 

323-1. 

323-2. 

350-1. 



TABLES 

Table 110-1 
Table 111-1. 
Table 124-1. 
Table 125-1. 
Table 232-1. 

Table 232-2. 



Table 232-3. 
Table 232-4. 
Table 233-1. 

Table 233-2. 

Table 233-3. 
Table 234-1. 



Sag and Apparent Sag Sec. 2 

Safety Clearance to Electric Supply Station Fences 110A2 

Clearance From Live Parts 124A1 

Railing Used as Guards 124C3 

Use of Clearance Envelope and Conductor Movement 

Envelopes to Determine Applicable Clearance 233A 

Conductor Movement Envelope 233Ala 

Clearance Envelope 233B 

Clearance Diagram for Building 234A3 

Clearance Diagram for Other Structures 234A3 

Transitional Clearance When H is Greater Than V 234 

Clearances of Service Drop Terminating on Support Mast 234C3d(l)(b) 

Swimming Pool Clearances 234E3 

Clearance Envelope for Grain Bins Filled by Permanently Installed 

Augers, Conveyors, or Elevators 234F2c 

Clearance Envelope for Grain Bins Filled by 

Portable Augers, Conveyors, or Elevators 234F2a 

Rail Car Clearances 2341 

Clearance Diagram for Energized Conductor 235D 

Rule 236G, Exception 3 236G 

Obstruction of Working Space by Buckarm 237D1 

General Loading Map of United States With Respect to 

Loading of Overhead Lines 250B 

Basic Wind Speeds (miles per hour) 250C 

Basic Wind Speeds 250C 

Western Gulf of Mexico Hurricane Coastline 250C 

Eastern Gulf of Mexico and Southeastern US Hurricane Coastline.. 250C 

Mid and Northern Atlantic Hurricane Coastline 250C 

Roadway Vehicle Load 323A1 

Wheel Load Area 323A1 

Symbols for Identification of Buried Cables 350G 

Values for Use with Fig 110-1 11B2 

Illumination Levels 111A 

Clearance From Live Parts 124A1 

Working Space 125 A3 

Vertical Clearance of Wires, Conductors, and Cables 

Above Ground, Roadway, Rail, or Water Surfaces 232B1 

Vertical Clearance of Equipment Cases, Support Arms, Platforms, 
Braces and Unguarded Rigid Live Parts Above Ground, Roadway, 

or Water Surfaces 232B2 

Reference Heights 232D2 

Electrical Component of Clearance in Rule 232D3a 232D3a 

Vertical Clearance Between Wires, Conductors, and 

Cables Carried on Different Supporting Structures 233C1 

Clearance Between Supply Wires, Conductors, and 

Cables in Rule 233C3b(l) 233C3b(l) 

Reference Heights 233C3a 

Clearance of Wires, Conductors, Cables, and Unguarded 
Rigid Live Parts Adjacent but Not Attached to Buildings 
and Other Installations Except Bridges 234Cla 

xxix 
Copyright © 2001 IEEE. All rights reserved. 



10 
29 
36 

44 

86 
87 
89 
97 
97 
97 
108 
109 

115 

116 
119 

134 
145 
146 

162 
166 
167 
168 
169 
169 
197 
197 
205 



29 
31 

37 
45 

74 



81 

83 
84 

91 

94 
95 



104 



I 



Contents 
TABLES RULE PAGE 

Table 234-2 . Clearance of Wires , Conductors , Cables , and Unguarded 

Rigid Live Parts From Bridges 234Dla 110 

Table 234-3. Clearance of Wires, Conductors, Cables or Unguarded Rigid Live 

Parts Over or Near Swimming Pools 234E1 1 13 

Table 234-4. Electrical Component of Clearance of Buildings, Bridges, 

and Other Installations 234H3a 

Table 234-5. Reference Distances 234H2 121 

Table 235-1 . Horizontal Clearance Between Wires, Conductors, or 

Cables at Supports 235Bla 123 

Table 235-2. Horizontal Clearances Between Line Conductors Smaller 

Than AWG No. 2 at Supports, Based on Sags 235Blb(l) 124 

Table 235-3. Horizontal Clearances Between Line Conductors 

AWG No. 2 or Larger at Supports, Based on Sags 235Blb(2) 125 

Table 235-4. Electrical Clearances in Rule 235B3a(l) 235B3a(l) 128 

Table 235-5. Vertical Clearance Between Conductors at Supports 235C1 131 

Table 235-6. Clearance in Any Direction From Line Conductors to 

Supports and to Vertical or Lateral Conductors, Span, 

or Guy Wires Attached to the Same Support 235E1 135 

Table 235-7. Clearance in Any Direction From Line Conductors to 

Supports 235E3b 140 

Table 236- 1 . Horizontal Clearance Between Conductors Bounding the 

Climbing Space 236E 143 

Table 238-1 . Vertical Clearance Between Supply Conductors and 

Communications Equipment, Between Communication 

Conductors and Supply Equipment, and Between Supply 

and Communications Equipment 238B 148 

Table 238-2. Vertical Clearance of Span Wires and Brackets From 

Communication Lines 238C 148 

Table 239-1. Clearance of Open Vertical and Lateral Conductors 239E1 153 

Table 239-2. Clearance Between Open Vertical Conductors and Pole 

Surface 239E2a(l) 154 

Table 242- 1 . Grades of Construction for Supply Conductors Alone, 

at Crossing, or on the Same Structures With Other 

Conductors 242 157 

Table 242-2. Grades of Construction for Communication Conductors Alone, 

or in Upper Position of Crossing or on Joint Poles 242 159 

Table 250-1 . Ice, Wind, and Temperature 250C 162 

Table 250-2 . Velocity Pressure Exposure Coefficient k z , Structure and Wire 250C 163 

Table 250-3 Structure and Wire Gust Response Factors, Grp 250C 164 

Table 251-1. Temperatures and Constants 251B3 170 

Table 253-1 . Overload Factors for Structures, Crossarms, Support Hardware, Guys, 

Foundation, and Anchors to Be Used with the Strength Factors of 

Table 261-1A 253 173 

Table 253-2. Alternate Overload Factors for Wood and Reinforced (Not Prestressed) 

Concrete Structures to Be Used with the Strength Factors of 

Table 261-1B 253 174 

Table 261-1A. Strength Factors for Structures, Crossarms, Support Hardware, Guys, 

Foundations, and Anchors for Use with Overload Factors of 

Table 253-1 261M 182 

Table 261 - IB . Strength Factors for Structures and Crossarms for Use 

with Overload Factor of Table 253-2 261D2 182 

Table 261-2 Dimensions of Crossarm Cross Section of Select Southern Pine 

and Douglas Fir 261D2 183 

xxx 
Copyright © 2001 IEEE. All rights reserved. 



Contents 



Table 263- 1 . Sizes for Grade N Supply Line Conductors (AWG for 

Copper and Aluminum, Stl WG for Steel) 263D1 184 

Table 263-2. Sizes of Service Drops of 750 V or Less 263Ela(l) 185 

Table 273-1 . Insulation Level Requirements 273 188 

Table 341-1 . Clearance Between Supply and Communications Facilities 

in Joint-Use Manholes and Vaults 341B2b(5) 202 

Table 352-1. Supply Cable or Conductor Burial Depth 352D2 206 

Table 43 1 - 1 . Overhead Supply Lines and Equipment Minimum Approach 

Distances to Exposed Energized Parts 431 225 

Table 441-1. AC Live Work Minimum Approach Distance 441 A4 228 

Table 44 1 -2 . AC Live Work Minimum Approach Distance 

With Transient Overvoltage Factor 441 A4 229 

Table 44 1 -3 . AC Live Work Minimum Approach Distance 

With Transient Overvoltage Factor 441A4 231 

Table 441-4. DC Live Work Minimum Approach Distance 

With Transient Overvoltage Factor 441A1 233 

Table 441-5. Altitude Correction Factor 441A4 234 

Table 44 1 -6 Maximum Use Voltage for Rubber Insulating Equipment 44 1 A4 234 



I 



XXXI 



Copyright © 2001 IEEE. All rights reserved. 



APPENDIX PAGE 

Appendix A Uniform System of Clearances Adopted in the 1990 Edition 

Introduction 243 

The 1990 Changes 243 

Clearance Rules and Tables Prior to 1990 249 

Clearance Values Prior to 1990 253 

Summary— Prior Editions 253 

Clearances Subcommittee Activities 253 

Summary 253 

Appendix B Bibliography 254 

APPENDIX FIGURES 

Figure Al . Clearance at Maximum Sag 248 

Figure A2. Basic Clearance 250 

Figure A3 . Additional Clearance Required for High-Temperature Operation 25 1 

Figure A4. Additional Clearance Required for Long-Span Construction 252 

APPENDIX TABLES 

Table A- 1. 245 

Table A-2a. Reference Components of Rule 232 246 

Table A-2b. Reference Components of Rule 234 247 

Index 257 

Revision Procedures 279 

Form for Change Proposal 281 

Time Schedule 282 

Working Group Assignments 283 

Tentative Interim Amendments 286 



xxxn 
Copyright © 2001 IEEE. All rights reserved. 



Letter Symbols for Units 



This code uses standard symbols for units. They have the following meanings: 



I 



A 


ampere 


C 


degree Celsius 


ft 


foot 


ft 2 


square foot 


ft 3 


cubic foot 


F 


degree Farenheit 


g 


gram 


Hz 


hertz 


h 


hour 


in 


inch 


in2 


square inch 


k 


kilo (103) 


kg 


kilogram 


kPa 


kilo pascal 


km 2 


square kilometer 


kV 


kilovolt (1000 volts) 


kVA 


kilovoltampere 


kW 


kilowatt 


m 


meter 


m 2 


square meter 


m 3 


cubic meter 


m 


milli (10-3) 


mA 


milliampere 


mi 


mile (statute) 


| mm 


millimeter 


min 


minute (time) 


N 


newton 


Pa 


pascal 


lb 


pound 


s 


second (time) 


V 


volt 


W 


watt 



XXXlll 

Copyright © 2001 IEEE. All rights reserved. 



XXXIV 

Copyright © 2001 IEEE. All rights reserved. 



010 SECTION 1. INTRODUCTION 013A1 



Section 1. 
Introduction to the 

National Electrical Safety Code® 

010. Purpose 

The purpose of these rules is the practical safeguarding of persons during the installation, operation, 
or maintenance of electric supply and communication lines and associated equipment. 

These rules contain the basic provisions that are considered necessary for the safety of employees 
and the public under the specified conditions. This code is not intended as a design specification or as 
an instruction manual. 

Oil. Scope 

| A. These rules cover supply and communication lines, equipment, and associated work practices em- 
ployed by a public or private electric supply, communications, railway, or similar utility in the exercise 
of its function as a utility. They cover similar systems under the control of qualified persons, such as 
those associated with an industrial complex or utility interactive system. 

B . The NESC covers utility facilities and functions up to the service point. 

NOTE: The National Electrical Code® (NEC®), NFPA 70-1999 1 covers utilization wiring requirements beyond 
the service point. 

C. NESC rules cover street and area lights (supplied by underground or overhead conductors) under the 
exclusive control of utilities (including their authorized contractors) or other qualified persons (such 
as those associated with an industrial complex). 

NOTE: Luminaires not under such exclusive control are governed by the requirements of the NEC. 

D. NESC rules do not cover installations in mines, ships, railway rolling equipment, aircraft, or automo- 
tive equipment, or utilization wiring except as covered in Parts 1 and 3. 

012. General Rules 

A. All electric supply and communication lines and equipment shall be designed, constructed, operated, 
and maintained to meet the requirements of these rules. 

B. The utilities, authorized contractors, or other entities, as applicable, performing design, construction, 
operation, or maintenance tasks for electric supply or communication lines or equipment covered by 
this code shall be responsible for meeting applicable requirements. 

C. For all particulars not specified in these rules, construction and maintenance should be done in accor- 
dance with accepted good practice for the given local conditions known at the time by those respon- 
sible for the construction or maintenance of the communication or supply lines and equipment. 

013. Application 

A. New Installations and Extensions 

1 . These rules shall apply to all new installations and extensions, except that they may be waived or 
modified by the administrative authority. When so waived or modified, safety shall be provided in 
other ways. 

EXAMPLE: Alternative working methods, such as the use of barricades, guards, or other electrical protective 
equipment, may be implemented along with appropriate alternative working clearances as a means of provid- 
ing safety when working near energized conductors. 



I 



'information on references can be found in Section 3. 



1 
Copyright © 2001 IEEE. All rights reserved. 



013A2 SECTION 1. INTRODUCTION 015F 



2. Types of construction and methods of installation other than those specified in the rules may be 
used experimentally to obtain information, if done where 

a. Qualified supervision is provided, 

b. Equivalent safety is provided, and 

c. On joint use facilities, all affected parties agree. 

B . Existing Installations 

1 . Where an existing installation meets, or is altered to meet, these rules, such installation is consid- 
ered to be in compliance with this edition and is not required to comply with any previous edition. 

2. Existing installations, including maintenance replacements, that currently comply with prior edi- 
tions of the Code, need not be modified to comply with these rules except as may be required for 
safety reasons by the administrative authority. 

3 . Where conductors or equipment are added, altered, or replaced on an existing structure, the struc- 
ture or the facilities on the structure need not be modified or replaced if the resulting installation 
will be in compliance with either (a) the rules that were in effect at the time of the original instal- 
lation, or (b) the rules in effect in a subsequent edition to which the installation has been previously 
brought into compliance , or (c) the rules of this edition in accordance with Rule 1 3B 1 . 

014. Waiver 

The person responsible for an installation may modify or waive rules in the case of emergency or tem- 
porary installations. 

A. Emergency Installations 

1. The clearances required in Section 23 may be decreased for emergency installations. See Rule 
230A. 

2. The strength of material and construction for emergency installations shall be not less than that 
required for Grade N construction. See Rule 263. 

3. Emergency installations shall be removed, replaced, or relocated, as desired, as soon as practical. 

B. Temporary Overhead Installations 

When an installation is temporary, or where facilities are temporarily relocated to facilitate other 
work, the installation shall meet the requirements for non-temporary installation except that the 
strength of material and construction shall be not less than that required for Grade N construction. See 
Rule 263. 

015. Intent 

A. The word "shall" indicates provisions that are mandatory. 

B . The word "should" indicates provisions that are normally and generally practical for the specified 
conditions. However, where the word "should" is used, it is recognized that, in certain instances, ad- 
ditional local conditions not specified herein may make these provisions impractical. When this oc- 
curs, the difference in conditions shall be appropriately recognized and Rule 012 shall be met. 

C. Footnotes to a table have the force and effect required or allowed by the rule that specifies the use of 
the table. 

D. Exceptions to a rule have the same force and effect required or allowed by the rule to which the ex- 
ception applies. 

E. The word "RECOMMENDATION" indicates provisions considered desirable, but that are not intend- 
ed to be mandatory. 

F. The word "NOTE" or the word "EXAMPLE" used in a rule indicates material provided for informa- 
tion or illustrative purposes only. "NOTES" and "EXAMPLES" are not mandatory and are not con- 
sidered to be a part of Code requirements. 

2 
Copyright © 2001 IEEE. All rights reserved. 



015G SECTION 1. INTRODUCTION 017B 



G. A "RECOMMENDATION," "EXCEPTION," or "NOTE" applies to all text in that rule above its lo- 
cation that is indented to the same level. 

016. Effective Date 

This edition may be used at any time on or after the publication date. Additionally, this edition shall 
become effective no later than 180 days following its publication date for application to new installa- 
tions and extensions where both design and approval were started after the expiration of that period, 
unless otherwise stipulated by the administrative authority. 

NOTE: A period of 180 days is allowed for utilities and regulatory authorities to acquire copies of the new edition 
and to change regulations, internal standards, and procedures as may be required. There is neither an intention to 
require or imply that this edition be implemented before 180 days from the publication date, nor an intention to 
prohibit earlier implementation. 

017. Units of Measure 

A. Numerical values in the requirements of this code are stated in the metric system 2 and in the custom- 
ary inch-foot-pound system. In text, the metric value is shown first with the customary inch-foot- 
pound (inside parentheses) following. Extensive detailed tables are duplicated. The first, marked m, 
contains metric (SI) values; the second, marked in, ft, or lb, contains the inch-foot-pound values. Ten- 
sions and wind loads are stated in newtons, the SI unit of force. 

The SI values and the customary inch-foot-pound values are not, nor are they intended to be, iden- 
tical measures. The values shown in each system of measurement have been rounded to convenient 
numbers in order to simplify measurement and to minimize errors. The values shown in each system 
are functional equivalents for safety purposes. 

The values required in this code have been carefully developed and evaluated to ensure that the 
intended levels of safety are provided in both systems; neither is distinguishable from the other for 
safety purposes. The values specified in either system of measurement may be used, or the values of 
the two systems may be intermixed, as desired. 

B . The dimensions of physical items referenced in this code, such as wires and ground rods , are "nominal 
values" assigned for the purpose of convenient designation . Due to manufacturing limitations or other 
restraints, other standards may set tolerances, variations, or ranges for the dimensions of such items. 



I 



2 Le Systeme Internationale d' Unites (The International System of Units [or SI] in the modern version of the metric system). For basic 

information and conversion factors, see EEEE/ASTM SI 10-1997 [B21], listed in Appendix B. 

3 It is recognized that many equivalent utility system components may be purchased in both SI and customary units. 

3 
Copyright © 2001 IEEE. All rights reserved. 



adm SECTION 2. DEFINITIONS 

Section 2. 
Definitions of Special Terms 



The following definitions are for use with the National Electrical Safety Code. For other use, and for def- 
initions not contained herein, see The Authoritative Dictionary of IEEE Standards Terms, Seventh Edition. 

administrative authority. The governmental authority exercising jurisdiction over application of this code. 
I 

ampacity. The current-carrying capacity , expressed in amperes, of an electric conductor under stated thermal 
conditions. 

anchorage. A secure point of attachment to which the fall protection system is connected. 

automatic. Self-acting, operating by its own mechanism when actuated by some impersonal influence— as, 
for example, a change in current strength; not manual; without personal intervention. Remote control that 
requires personal intervention is not automatic, but manual. 

backfill (noun). Materials such as sand, crushed stone, or soil, that are placed to fill an excavation. 

ballast section (railroads). The section of material, generally trap rock, that provides support under railroad 
tracks. 

bonding. The electrical interconnecting of conductive parts, designed to maintain a common electrical 
potential. 

cable. A conductor with insulation, or a stranded conductor with or without insulation and other coverings 
(single-conductor cable), or a combination of conductors insulated from one another (multiple-conductor 
cable). 

cable jacket. A protective covering over the insulation, core, or sheath of a cable. 

cable sheath. A conductive protective covering applied to cables. 

NOTE: A cable sheath may consist of multiple layers, of which one or more is conductive. 

cable terminal. A device that provides insulated egress for the conductors. Syn: termination. 

circuit. A conductor or system of conductors through which an electric current is intended to flow. 

circuit breaker. A switching device capable of making, carrying, and breaking currents under normal circuit 
conditions and also making, carrying for a specified time, and breaking currents under specified abnormal 
conditions such as those of short circuit. 

clearance. The clear distance between two objects measured surface to surface. 

climbing. The vertical movement (ascending and descending) and horizontal movement to access or depart 
the worksite. 

common use. Simultaneous use by two or more utilities of the same kind. 

communication lines. See: lines. 

4 
Copyright © 2001 IEEE. All rights reserved. 



SECTION 2 . DEFINITIONS duc 



conductor. 

1 . A material, usually in the form of a wire, cable, or bus bar, suitable for carrying an electric current. 

2. bundled conductor. An assembly of two or more conductors used as a single conductor and employ- 
ing spacers to maintain a predetermined configuration. The individual conductors of this assembly are called 
subconductors. 

3. covered conductor. A conductor covered with a dielectric having no rated insulating strength or hav- 
ing a rated insulating strength less than the voltage of the circuit in which the conductor is used. 

4. fiber-optic conductor. See: fiber-optic cable— communication or fiber-optic cable— supply. 

5. grounded conductor. A conductor that is intentionally grounded, either solidly or through a noninter- 
rupting current-limiting device. 

6. grounding conductor. A conductor that is used to connect the equipment or the wiring system with a 
grounding electrode or electrodes. 

7. insulated conductor. A conductor covered with a dielectric (other than air) having a rated insulating 
strength equal to or greater than the voltage of the circuit in which it is used. 

8. lateral conductor. A wire or cable extending in a general horizontal direction at an angle to the general 
direction of the line conductors, and entirely supported on one structure. 

9. line conductor. (Overhead supply or communication lines.) A wire or cable intended to carry electric 
currents , extending along the route of the line , supported by poles , towers , or other structures , but not includ- 
ing vertical or lateral conductors. 

10. open conductor. A type of electric supply or communication line, construction in which the conduc- 
tors are bare, covered, or insulated and without grounded shielding, individually supported at the structure 
either directly or with insulators. Syn: open wire. 

conductor shielding. An envelope that encloses the conductor of a cable and provides an equipotential sur- 
face in contact with the cable insulation. 

conduit. A structure containing one or more ducts. 

NOTE: Conduit may be designated as iron-pipe conduit, tile conduit, etc. If it contains only one duct it is called single- 
duct conduit; if it contains more than one duct it is called multiple-duct conduit, usually with the number of ducts as a 
prefix, for example, two-duct multiple conduit. 

conduit system. Any combination of duct, conduit, conduits, manholes, handholes, and vaults joined to form 
an integrated whole. 

current-carrying part. A conducting part intended to be connected in an electric circuit to a source of volt- 
age. Non-current-carrying parts are those not intended to be so connected. 

de-energized. Disconnected from all sources of electrical supply by open switches, disconnectors, jumpers, 
taps, or other means. 

NOTE: De-energized conductors or equipment could be electrically charged or energized through various means, such 
as induction from energized circuits, portable generators, lightning, etc. 

designated person. A qualified person designated to perform specific duties under the conditions existing. 
Syn: designated employee. 

disconnecting or isolating switch. A mechanical switching device used for changing the connections in a 
circuit or for isolating a circuit or equipment from a source of power. 

NOTE: It is required to carry normal load current continuously as well as abnormal or short-circuit current for short in- 
tervals, as specified. It is also required to open or close circuits either when negligible current is broken or made, or when 
no significant change in the voltage across the terminals of each of the switch poles occurs. Syn: disconnector, isolator. 



I 



duct. A single enclosed raceway for conductors or cable. 



5 
Copyright © 2001 IEEE. All rights reserved. 



e ff SECTION 2. DEFINITIONS 8 en 



effectively grounded. Intentionally connected to earth through a ground connection or connections of 
sufficiently low impedance and having sufficient current-carrying capacity to limit the buildup of voltages to 
levels below that which may result in undue hazard to persons or to connected equipment. 

electric supply equipment. Equipment that produces, modifies, regulates, controls, or safeguards a supply 
of electric energy. Syn: supply equipment. 

electric supply lines. See: lines. 

electric supply station. Any building, room, or separate space within which electric supply equipment is 
located and the interior of which is accessible, as a rule, only to qualified persons. This includes generating 
stations and substations, including their associated generator, storage battery, transformer, and switchgear 
rooms or enclosures, but does not include facilities such as pad-mounted equipment and installations in 
manholes and vaults. 

1 . generating station. A plant wherein electric energy is produced by conversion from some other form 
of energy (for example, chemical, nuclear, solar, mechanical, or hydraulic) by means of suitable apparatus. 
This includes all generating station auxiliaries and other associated equipment required for the operation of 
the plant. Not included are stations producing power exclusively for use with communications systems. 

2. substation. An enclosed assemblage of equipment, e.g., switches, circuit breakers, buses, and trans- 
formers, under the control of qualified persons, through which electric energy is passed for the purpose of 
switching or modifying its characteristics. 

enclosed. Surrounded by case, cage, or fence designed to protect the contained equipment and limit the like- 
lihood, under normal conditions, of dangerous approach or accidental contact by persons or objects. 

energized. Electrically connected to a source of potential difference, or electrically charged so as to have a 
| potential significantly different from that of earth in the vicinity. Syn: live. 

equipment. A general term including fittings, devices, appliances, fixtures, apparatus, and similar terms used 
as part of or in connection with an electric supply or communications system. 

exposed. Not isolated or guarded. 

fall arrest system. The assemblage of equipment, such as a line-worker's body belt, aerial belt, or full body 
harness in conjunction with a connecting means, with or without an energy absorbing device, and an anchor- 
age to limit the forces a worker can experience during a fall. 

fall prevention system. A system, which may include a positioning device system, intended to prevent a 
worker from falling from an elevation. 

fall protection program. A program intended to protect workers from injury due to falls from elevations. 

fall protection system (hardware). Consists of either a fall prevention system or a fall arrest system. 

fiber-optic cable— communication. A fiber optic cable meeting the requirements for a communication line 
and located in the communication space of overhead or underground facilities. 

fiber-optic cable— supply. A fiber-optic cable located in the supply space of overhead or underground 
facilities. 

fireproofing (of cables). The application of a fire-resistant covering. 

generating station. See: electric supply station. 

6 
Copyright © 2001 IEEE. All rights reserved. 



gro SECTION 2. DEFINITIONS '"" 



grounded. Connected to or in contact with earth or connected to some extended conductive body that serves 
instead of the earth. 

grounded effectively. See: effectively grounded. 

grounded system. A system of conductors in which at least one conductor or point is intentionally grounded, 
either solidly or through a noninterrupting current-limiting device. 

guarded. Covered, fenced, enclosed, or otherwise protected, by means of suitable covers or casings, barrier 
rails or screens, mats or platforms, designed to limit the likelihood, under normal conditions, of dangerous 
approach or accidental contact by persons or objects. 

NOTE: Wires that are insulated but not otherwise protected are not normally considered to be guarded. See exceptions 
under applicable rules. 

handhole. An access opening, provided in equipment or in a below-the-surface enclosure in connection with 
underground lines, into which personnel reach but do not enter, for the purpose of installing, operating, or 
maintaining equipment or cable or both. 

harness. A component with a design of straps that is fastened about the worker in a manner so as to contain 
the torso and distribute the fall arrest forces over at least the upper thighs, pelvis, chest, and shoulders with 
means for attaching it to other components and subsystems. 
NOTE: Wherever the word "harness" is used in this code, it refers to full body harness. 

in service. Lines and equipment are considered in service when connected to the system and intended to be 
capable of delivering energy or communication signals, regardless of whether electric loads or signaling ap- 
paratus are presently being served from such facilities. 

insulated. Separated from other conducting surfaces by a dielectric (including air space) offering a high re- 
sistance to the passage of current. 

NOTE: When any object is said to be insulated, it is understood to be insulated for the conditions to which it is normally 
subjected. Otherwise, it is, within the purpose of these rules, uninsulated. 

insulation (as applied to cable). That which is relied upon to insulate the conductor from other conductors 
or conducting parts or from ground. 

insulation shielding. An envelope that encloses the insulation of a cable and provides an equipotential sur- 
face in contact with the cable insulation. 

insulator. Insulating material in a form designed to support a conductor physically and electrically separate 
it from another conductor or object. 

isolated. Not readily accessible to persons unless special means for access are used. 

isolated by elevation. Elevated sufficiently so that persons may safely walk underneath. 

isolator. See: disconnecting or isolating switch. 

jacket. A protective covering over the insulation, core, or sheath of a cable. 

joint use. Simultaneous use by two or more kinds of utilities. 

lanyard. A flexible line or webbing, rope, wire rope, or strap that generally has a connector at each end for 
connecting the line-worker's body belt, aerial belt, or full body harness to an energy absorbing device, life- 
line, or anchorage. 

7 
Copyright © 2001 IEEE. All rights reserved. 



I 



lim SECTION 2. DEFINITIONS P ad 



limited access highways. As used herein, limited access highways are fully controlled highways where 
access is controlled by a governmental authority for purposes of improving traffic flow and safety. Fully 
controlled access highways have no grade crossings and have carefully designed access connections. 

lines. 

1 . communication lines. The conductors and their supporting or containing structures that are used for 
public or private signal or communications service, and which operate at potentials not exceeding 400 V to 
ground or 750 V between any two points of the circuit, and the transmitted power of which does not exceed 

| 150 W. When operating at not more than 90 V ac or 150 V dc, no limit is placed on the transmitted power of 
the system. Under specified conditions, communication cables may include communication circuits 
exceeding the preceding limitation where such circuits are also used to supply power solely to 
communications equipment. 

NOTE: Telephone, telegraph, railroad-signal, data, clock, fire, police-alarm, cable-television, and other systems 
conforming with the above are included. Lines used for signaling purposes, but not included under the above definition, 
are considered as supply lines of the same voltage and are to be so installed. 

2. electric supply lines. Those conductors used to transmit electric energy and their necessary supporting 
or containing structures. Signal lines of more than 400 V are always supply lines within the meaning of the 
rules, and those of less than 400 V may be considered as supply lines, if so run and operated throughout. 
Syn: supply lines. 

line-worker's body belt. A belt that consists of a belt strap and D-rings and which may include a cushion 
section or a tool saddle. 

| live. See: energized. 

manhole. A subsurface enclosure that personnel may enter used for the purpose of installing, operating, and 
maintaining submersible equipment and cable. 

manhole cover. A removable lid that closes the opening to a manhole or similar subsurface enclosure. 

manhole grating. A grid that provides ventilation and a protective cover for a manhole opening. 

manual. Capable of being operated by personal intervention. 

minimum approach distance. The closest distance a qualified employee is permitted to approach either an 
energized or a grounded object, as applicable for the work method being used. 

multigrounded/multiple grounded system. A system of conductors in which a neutral conductor is inten- 
tionally grounded solidly at specified intervals. A multigrounded or multiple grounded system may or may 
not be effectively grounded. See: effectively grounded. 

neutral conductor. A system conductor other than a phase conductor that provides a return path for current 
to the source. Not all systems have a neutral conductor. An example is an ungrounded delta system containing 
only three energized phase conductors. 

out of service. Lines and equipment are considered out of service when disconnected from the system and 
when not intended to be capable of delivering energy or communications signals. 

pad-mounted equipment. A general term describing enclosed equipment, the exterior of which enclosure is 
at ground potential, positioned on a surface-mounted pad. 

8 
Copyright © 2001 IEEE. All rights reserved. 



P° s SECTION 2. DEFINITIONS sa S 



positioning device system. A system of equipment or hardware that, when used with its line-worker's body 
belt or full body harness, allows a worker to be supported on an elevated vertical surface, such as a pole or 
tower, and work with both hands free. 

positioning strap. A strap with snaphook(s) to connect to the D-rings of a line-worker's body belt or full 
body harness. 

prestressed-concrete structures. Concrete structures that include metal tendons that are tensioned and an- 
chored either before or after curing of the concrete. 

pulling iron. An anchor secured in the wall, ceiling, or floor of a manhole or vault to attach rigging used to 
pull cable. 

pulling tension. The longitudinal force exerted on a cable during installation. 

qualified. Having been trained in and having demonstrated adequate knowledge of the installation, construc- 
tion, or operation of lines and equipment and the hazards involved, including identification of and exposure 
to electric supply and communication lines and equipment in or near the workplace. An employee who is un- 
dergoing on-the-job training and who, in the course of such training, has demonstrated an ability to perform 
duties safely at his or her level of training, and who is under the direct supervision of a qualified person, is 
considered to be a qualified person for the performance of those duties. 

qualified climber. A worker who, by reason of training and experience, understands the methods and has 
routinely demonstrated proficiency in climbing techniques and familiarity with the hazards associated with 
climbing. 

raceway. Any channel designed expressly and used solely for holding conductors. 

random separation. Installed with no deliberate separation. 

readily climbable supporting structure. A supporting structure having sufficient handholds and footholds 
that the structure can be climbed easily by an average person without using a ladder, special tools or devices, 
or extraordinary physical effort. A supporting structure with a space of 2.45 m (8 ft) or more between hand- 
holds and footholds starting not more than 1.80 m (6 ft) above grade is not readily climbable. 
NOTE 1: Round poles, diagonal braces on towers, and guy wires are not considered to be readily climbable. 
NOTE 2: Diagonal braces on towers are not considered to be handholds or footholds except that, at their point of attach- 
ment to a vertical structural member, they may create a foothold. 

remotely operable (as applied to equipment). Capable of being operated from a position external to the 
structure in which it is installed or from a protected position within the structure. 

roadway. The portion of highway, including shoulders, for vehicular use. See also: shoulder; traveled way. 

NOTE: A divided highway has two or more roadways. 

rural districts. All places not urban. This may include thinly settled areas within city limits. 

sag. 

1 . The distance measured vertically from a conductor to the straight line joining its two points of support. 
Unless otherwise stated in the rule, the sag referred to is the sag at the midpoint of the span. See Fig D-l . 

2. initial unloaded sag. The sag of a conductor prior to the application of any external load. 



I 



9 
Copyright © 2001 IEEE. All rights reserved. 



sag 



SECTION 2. DEFINITIONS 



shi 



3. final sag. The sag of a conductor under specified conditions of loading and temperature applied, after it 
has been subjected for an appreciable period to the loading prescribed for the loading district in which it is 
situated, or equivalent loading, and the loading removed. Final sag shall include the effect of inelastic defor- 
mation (creep) . 

4. final unloaded sag. The sag of a conductor after it has been subjected for an appreciable period to the 
loading prescribed for the loading district in which it is situated, or equivalent loading, and the loading re- 
moved. Final unloaded sag shall include the effect of inelastic deformation (creep). 

5. total sag. The distance measured vertically from the conductor to the straight line joining its two points 
of support, under conditions of ice loading equivalent to the total resultant loading for the district in which it 
is located. 

6. maximum total sag. The total sag at the midpoint of the straight line joining the two points of support 
of the conductor. 

7. apparent sag of a span. The maximum distance between the wire in a given span and the straight line 
between the two points of support of the wire, measured perpendicularly from the straight line. See Fig D-l . 

8. sag of a conductor at any point in a span. The distance measured vertically from the particular point 
in the conductor to a straight line between its two points of support. 

9. apparent sag at any point in the span. The distance, at the particular point in the span, between the wire 
and the straight line between the two points of support of the wire, measured perpendicularly from the straight 
line. 

STRAIGHT LINE BETWEEN 
POINTS OF SUPPORT — 



MIDPOINT 
APPARENT SAG 




SLOPING SPAN 



Fig D-l 
Sag and Apparent Sag 



separation. The distance between two objects, measured surface to surface, and usually filled with a solid or 
liquid material. 

service drop. The overhead conductors between the electric supply or communication line and the building or 
structure being served. 

service point. The point of connection between the facilities of the serving utility and the premises wiring. 



shield wire/conductor (also referred to as static wire or ground wire). A grounded conductor installed to 
shield transmission or distribution phase conductors from direct lightning strikes. 

10 
Copyright © 2001 IEEE. All rights reserved. 



sho SECTION 2. DEFINITIONS tra 



shoulder. The portion of the roadway contiguous with the traveled way for accommodation of stopped vehi- 
cles for emergency use and for lateral support of base and surface course. 

side-wall pressure. The crushing force exerted on a cable during installation. 

single grounded system/unigrounded system. A system of conductors in which one conductor is intention- 
ally grounded solidly at a specific location, typically at the source. 

spacer cable. A type of electric supply-line construction consisting of an assembly of one or more covered 
conductors, separated from each other and supported from a messenger by insulating spacers. 

span length. The horizontal distance between two adjacent supporting points of a conductor. 

span wire. An auxiliary suspension wire that serves to support one or more trolley contact conductors or a 
light fixture and the conductors that connect it to a supply system. 

structure conflict. A line so situated with respect to a second line that the overturning of the first line will 
result in contact between its supporting structures or conductors and the conductors of the second line, assum- 
ing that no conductors are broken in either line. 

substation. See: electric supply station. 

supply equipment. See: electric supply equipment. 

supply station. See: electric supply station. 

supporting structure. The main supporting unit (usually a pole or tower). 

susceptiveness. The characteristics of a communication circuit, including its connected apparatus, that deter- 
mine the extent to which it is adversely affected by inductive fields. 

switch. A device for opening and closing or for changing the connection of a circuit. In these rules, a switch 
is understood to be manually operable, unless otherwise stated. 

switchboard. A type of switchgear assembly that consists of one or more panels with electric devices mount- 
ed thereon, and associated framework. 

tag. Accident prevention tag (DANGER, PEOPLE AT WORK, etc.) of a distinctive appearance used for the 
purpose of personnel protection to indicate that the operation of the device to which it is attached is restricted. 

termination. See: cable terminal. 

transferring (as applied to fall protection). The act of moving from one distinct object to another (e.g., be- 
tween an aerial device and a structure). 

transformer vault. An isolated enclosure either above or below ground with fire-resistant walls, ceiling, and 
floor, in which transformers and related equipment are installed, and which is not continuously attended dur- 
ing operation. See also: vault. 

transitioning (as applied to fall protection). The act of moving from one location to another on equipment 
or a structure. 



11 
Copyright © 2001 IEEE. All rights reserved. 



I 



tra SECTION 2. DEFINITIONS vo1 



traveled way. The portion of the roadway for the movement of vehicles, exclusive of shoulders and full-time 
parking lanes. 

ungrounded system. A system of conductors in which no conductor or point is intentionally grounded, ei- 
ther solidly or through a noninterrupting current-limiting device. 

unigrounded system. See: single grounded system/unigrounded system. 

unloaded tension. 

1 . initial. The longitudinal tension in a conductor prior to the application of any external load. 

2. final. The longitudinal tension in a conductor after it has been subjected for an appreciable period to 
the loading prescribed for the loading district in which it is situated, or equivalent loading, and the loading 
removed. Final unloaded tension shall include the effect of inelastic deformation (creep). 

urban districts. Thickly settled areas (whether in cities or suburbs) or where congested traffic often occurs. 
A highway, even though in thinly settled areas, on which the traffic is often very heavy, is considered as 
urban. 

utility. An organization responsible for the installation, operation, or maintenance of electric supply or com- 
munications systems. 

utility interactive system. An electric power production system that is operating in parallel with and capable 
of delivering energy to a utility electric supply system. 

utilization equipment. Equipment, devices, and connected wiring that utilize electric energy for mechani- 
cal, chemical, heating, lighting, testing, or similar purposes and are not a part of supply equipment, supply 
lines, or communication lines. 

vault. A structurally solid enclosure, including all sides, top, and bottom, above or below ground where entry 
is limited to personnel qualified to install, maintain, operate, or inspect the equipment or cable enclosed. The 
enclosure may have openings for ventilation, personnel access, cable entrance, and other openings required 
for operation of equipment in the vault. 

voltage. 

1. The effective (rms) potential difference between any two conductors or between a conductor and 
ground. Voltages are expressed in nominal values unless otherwise indicated. The nominal voltage of a sys- 
tem or circuit is the value assigned to a system or circuit of a given voltage class for the purpose of convenient 
designation. The operating voltage of the system may vary above or below this value. 

2. voltage of circuit not effectively grounded. The highest nominal voltage available between any two 
conductors of the circuit. 

NOTE: If one circuit is directly connected to and supplied from another circuit of higher voltage (as in the case of an 
autotransformer), both are considered to be of the higher voltage, unless the circuit of the lower voltage is effectively 
grounded, in which case its voltage is not determined by the circuit of higher voltage. Direct connection implies electric 
connection as distinguished from connection merely through electromagnetic or electrostatic induction. 

3 . voltage of a constant-current circuit. The highest normal full-load voltage of the circuit. 

4. voltage of an effectively grounded circuit. The highest nominal voltage available between any con- 
ductor of the circuit and ground unless otherwise indicated. 



12 
Copyright © 2001 IEEE. All rights reserved. 



vo1 SECTION 2. DEFINITIONS 



5. voltage to ground of: 

a. a grounded circuit. The highest nominal voltage available between any conductor of the circuit and 
that point or conductor of the circuit that is grounded. 

b. an ungrounded circuit. The highest nominal voltage available between any two conductors of the 
circuit concerned. 

6. voltage to ground of a conductor of: 

a. a grounded circuit. The nominal voltage between such conductor and that point or conductor of the 
circuit that is grounded. 

b. an ungrounded circuit. The highest nominal voltage between such conductor and any other con- 
ductor of the circuit concerned. 

wire gages. Throughout these rules the American Wire Gage (AWG), formerly known as Brown & Sharpe 
(B&S), is the standard gage for copper, aluminum, and other conductors, excepting only steel conductors, for 
which the Steel Wire Gage (Stl WG) is used. 
NOTE: The Birmingham Wire Gage is obsolete. 

worksite (as applied to fall protection). The location on the structure or equipment where, after the worker 
has completed the climbing (horizontally and vertically), the worker is in position to perform the assigned 
work or task. 



I 



13 
Copyright © 2001 IEEE. All rights reserved. 



SECTION 3. REFERENCES 

Section 3. 
References 



The following standards form a part of the National Electrical Safety Code to the extent indicated in the 
rules herein. 4 

ANSI C29. 1-1988, American National Standard Test Methods for Electrical Power Insulators. [Rules 272, 
273, and 277 NOTE la] 5 

ANSI C29 .2-1992, American National Standard for Wet-Process Porcelain and Toughened Glass Insulators 
(Suspension Type). [Rules 272 and 441B4c] 

ANSI C29 .3-1986 (R1995), American National Standard for Wet-Process Porcelain Insulators (Spool Type). 
[Rule 272] 

ANSI C29.4-1989 (R1995), American National Standard for Wet-Process Porcelain Insulators (Strain 
Type). [Rule 272] 

ANSI C29 .5-1984 (R1995), American National Standard for Low- and Medium- Voltage Pin Type Wet-Pro- 
cess Porcelain Insulators. [Rule 272] 

ANSI C29.6-1996, American National Standard for High- Voltage Pin Type Wet-Process Porcelain Insula- 
tors. [Rule 272] 

ANSI C29 .7-1996, American National Standard for High- Voltage Line-Post Type Wet-Process Porcelain In- 
sulators. [Rules 272 and 277 NOTE 2] 

ANSI C84. 1-1995 (R2001), American National Standard for Voltage Ratings for Electric Power Systems 
and Equipment (60 Hz). [Rule 441] 

ANSI 05. 1-1992, American National Standard Specifications and Dimensions for Wood Poles. [Rule 261] 

ANSI Z535 .1-1998, American National Standard for Safety Color Code. [Rule 1 10A1 NOTE, Rule 217Alc 
NOTE, Rule 323C4 NOTE, Rule 381G2 NOTE, and Rule 41 ID] 

ANSI Z535.2-1998, American National Standard for Environmental and Facility Safety Signs. [Rule 1 10A1 
NOTE, Rule 217Alc NOTE, Rule 323C4 NOTE, Rule 381G2 NOTE, and Rule 41 ID] 

ANSI Z535. 3- 1998, American National Standard for Criteria for Safety Symbols. [Rule 1 10A1 NOTE, Rule 
217Alc NOTE, Rule 323C4 NOTE, Rule 381G2 NOTE, and Rule 41 ID] 

ANSI Z535.4-1998, American National Standard for Product Safety Signs and Labels. [Rule 110A1 NOTE, 
Rule 217Alc NOTE, Rule 323C4 NOTE, Rule 381G2 NOTE, and Rule 41 ID] 

ANSI Z535.5-1998, American National Standard for Accident Prevention Tags (for Temporary Hazards). 
[Rule 1 10A1 NOTE, Rule 217Alc NOTE, Rule 323C4 NOTE, Rule 381G2 NOTE, and Rule 41 ID] 



The standards listed here were the editions used in this revision of the code. In some cases, newer editions may be in effect. Contact 
the publisher for information about availability. 

5 ANSI publications are available from the Sales Department, American National Standards Institute, 1 1 West 42nd Street, 13th Floor, 
New York, NY 10036, USA (http://www.ansi.org/). 

14 
Copyright © 2001 IEEE. All rights reserved. 



SECTION 3. REFERENCES 



ANSI/SIA A92.2-1990, American National Standard for Vehicle Mounted Elevating and Rotating Aerial 
Devices. [Rule 446] 

ASCE 7-1998, ASCE Standard for Minimum Design Loads for Buildings and Other Structures [250C] 6 



ASME B 15.1-2000, ASME Standard for Mechanical Power Transmission Apparatus. [Rule 122] 
ASTM D 178-1993 (R1998), ASTM Standard Specification for Rubber Insulating Matting. 7 [Rule 124] 

IEEE Std 4-1995, IEEE Standard Techniques for High-Voltage Testing. 8 [Rule 441] 
IEEE 100, The Authoritative Dictionary of IEEE Standards Terms, Seventh Edition. [Section 2, General] 
IEEE Std 516-1995, IEEE Guide for Maintenance Methods on Energized Power-Lines. [Rules 441 and 446] 
IEEE Std 1313-1993, IEEE Standard for Power Systems -Insulation Coordination. [Rule 124] 9 

NFPA 30-2000, Flammable and Combustible Liquids Code. 10 [Rule 127] 

NFPA 58-2001, Storage and Handling of Liquefied Petroleum Gases. [Rule 127] 

NFPA 59-2001, Storage and Handling of Liquefied Petroleum Gases at Utility Gas Plants. [Rule 127] 

NFPA 59A-2001 , Production, Storage, and Handling of Liquefied Natural Gas (LNG). [Rule 127] 

NFPA 70-1999, National Electrical Code (NEC). [Rules 01 1 , 124, and 127] 

NFPA 496-1998, Standard for Purged and Pressurized Enclosures for Electrical Equipment. [Rule 127] 

NFPA 8503-1997, Standard for the Installation and Operation of Pulverized Fuel Systems. [Rule 127] 



I 



6 ASCE publications are available from ASCE Publications, 1801 Alexander Bell Dr., Reston, VA 20191, (800) 548-ASCE (2723) 

(htrp://w w w .asce .org) . 

7 ASTM publications are available from the American Society for Testing and Materials, 100 Barr Harbor Drive, West Conshohocken, 

PA 19428-2959, USA (http://www.astm.org/). 

8 IEEE publications are available from the Institute of Electrical and Electronics Engineers, 445 Hoes Lane, P.O. Box 1331 , Piscataway, 

NJ 08855-1331, USA (http://standards.ieee.org/). 

9 IEEE Std 1313-1993 has been withdrawn; however, copies can be obtained from Global Engineering, 15 Inverness Way East, Engle- 

wood, CO 801 12-5704, USA, tel. (303) 792-2181 (http://globaljhs.com/). 

10 NFPA publications are available from Publications Sales, National Fire Protection Association, 1 Batterymarch Park, P.O. Box 9101 , 

Quincy, MA 02269-9101, USA. 

15 
Copyright © 2001 IEEE. All rights reserved. 



090 SECTION 9. GROUNDING METHODS 092B2b(2) 

Section 9. 

Grounding Methods for Electric Supply 

and Communications Facilities 



090. Purpose 

The purpose of Section 9 of this code is to provide practical methods of grounding , as one of the means 
of safeguarding employees and the public from injury that may be caused by electrical potential. 

091. Scope 

Section 9 of this code covers methods of protective grounding of supply and communication conduc- 
tors and equipment. The rules requiring grounding are in other parts of this code. 

These rules do not cover the grounded return of electric railways nor those lightning protection 
wires that are normally independent of supply or communication wires or equipment. 

092. Point of Connection of Grounding Conductor 

A. Direct Current Systems That Are to Be Grounded 

1. 750 V and below 

Connection shall be made only at supply stations. In three-wire dc systems, the connection shall 
be made to the neutral. 

2. Over 750 V 

Connection shall be made at both the supply and load stations. The connection shall be made to 
the neutral of the system. The ground or grounding electrode may be external to or remotely lo- 
cated from each of the stations. 

One of the two stations may have its grounding connection made through surge arresters pro- 
vided the other station neutral is effectively grounded as described above. 

EXCEPTION: Where the stations are not geographically separated as in back-to-back converter stations, the 
neutral of the system should be connected to ground at one point only. 

B. Alternating Current Systems That Are to Be Grounded 

1. 750 V and below 

The point of the grounding connection on a wye-connected three-phase four-wire system, or on a 
single-phase three-wire system, shall be the neutral conductor. On other one-, two-, or three-phase 
systems with an associated lighting circuit or circuits, the point of grounding connection shall be 
on the common circuit conductor associated with the lighting circuits. 

The point of grounding connection on a three-phase three-wire system, whether derived from 
a delta-connected or an ungrounded wye-connected transformer installation not used for lighting, 
may be any of the circuit conductors, or it may be a separately derived neutral. 

The grounding connections shall be made at the source, and at the line side of all service equip- 
ment. 

2. Over 750 V 

a. Nonshielded (Bare or Covered Conductors or Insulated Nonshielded Cables) 

Grounding connection shall be made at the neutral of the source. Additional connections may 
be made, if desired, along the length of the neutral, where this is one of the system conductors. 

b. Shielded 

( 1 ) Surge- Arrester Cable-Shielding Interconnection 

Cable-shielding grounds shall be bonded to surge-arrester grounds, where provided, at 
points where underground cables are connected to overhead lines. 

(2) Cable Without Insulating Jacket 

Connection shall be made to the neutral of the source transformer and at cable termination 
points. 

16 
Copyright © 2001 IEEE. All rights reserved. 



092B2b(3) SECTION 9. GROUNDING METHODS 092D3 



(3) Cable With Insulating Jacket 

Additional bonding and connections between the cable insulation shielding or sheaths and 
the system ground are recommended. In multi-grounded shielded cable systems, the 
shielding (including sheath) shall be grounded at each cable joint exposed to personnel 
contact. Where multi-grounded shielding cannot be used for electrolysis or sheath-current 
reasons, the shielding sheaths and splice-enclosure devices shall be insulated for the volt- 
age that may appear on them during normal operation. 

Bonding transformers or reactors may be substituted for direct ground connection at 
one end of the cable. 
3. Separate Grounding Conductor 

If a separate grounding conductor is used as an adjunct to a cable run underground, it shall be con- 
nected either directly or through the system neutral to the source transformers, source transformer 
accessories, and cable accessories where these are to be grounded. This grounding conductor shall 
be located in the same direct burial or duct bank run (or the same duct if this is of magnetic mate- 
rial) as the circuit conductors. 

EXCEPTION: The grounding conductor for a circuit that is installed in a magnetic duct need not be in the 
same duct if the duct containing the circuit is bonded to the separate grounding conductor at both ends. 

C. Messenger Wires and Guys 

1 . Messenger Wires 

Messenger wires required to be grounded shall be connected to grounding conductors at poles or 
structures at maximum intervals as listed below: 

a. Where messenger wires are adequate for system grounding conductors (Rules 093C1 , 093C2, 
and 093C5), four connections in each 1 .6 km (1 mi). 

b. Where messenger wires are not adequate for system grounding conductors, eight connections 
in each 1 .6 km (1 mi), exclusive of service grounds. 

2. Guys 

Guys that are required to be grounded shall be connected to one or more of the following: 

a. A grounded metallic supporting structure. 

b. An effective ground on a nonmetallic supporting structure. 

c. A line conductor that has at least four ground connections in each mile of line in addition to 
the ground connections at individual services. 

3. Common Grounding of Messengers and Guys on the Same Supporting Structure 

a. Where messengers and guys on the same supporting structure are required to be grounded, 
they shall be bonded together and grounded by connection to: 

(1) One grounding conductor that is grounded at that structure, or to 

(2) Separate grounding conductors or grounded messengers that are bonded together and 
grounded at that structure, or to 

(3) One or more grounded line conductors or grounded messengers that are (a) bonded 
together at this structure or elsewhere and (b) multi-grounded elsewhere at intervals as 
specified in Rules 092C1 and 092C2. 

b. At common crossing structures, messengers and guys that are required to be grounded shall be 
bonded together at that structure and grounded in accordance with Rule 092C3a. 
EXCEPTION: This rule does not apply to guys that are connected to an effectively grounded overhead 
static wire. 

D. Current in Grounding Conductor 

Ground connection points shall be so arranged that under normal circumstances there will be no ob- 
jectionable flow of current over the grounding conductor. If an objectionable flow of current occurs 
over a grounding conductor due to the use of multi-grounds, one or more of the following should be 
used: 

1 . Abandon one or more grounds . 

2 . Change location of grounds . 

3 . Interrupt the continuity of the conductor between ground connections. 

17 
Copyright © 2001 IEEE. All rights reserved. 



I 



092D4 SECTION 9. GROUNDING METHODS 093A 



4. Subject to the approval of the administrative authority, take other effective means to limit the 
current. 

The system ground of the source transformer shall not be removed. 

The temporary currents set up under abnormal conditions while the grounding conductors are per- 
forming their intended protective functions are not considered objectionable. The conductor shall 
have the capability of conducting anticipated fault current without thermal overloading or excessive 
voltage buildup. Refer to Rule 093C. 

E. Fences 

Fences that are required to be grounded by other parts of this code shall be designed to limit touch, 
step, and transferred voltages in accordance with industry practices. 

NOTE: IEEE Std 80-2000 [B22] 12 is one source that may be utilized to provide guidance in meeting these 
requirements. 

The grounding connections shall be made either to the grounding system of the enclosed equip- 
ment or to a separate ground. 

1 . Fences shall be grounded at each side of a gate or other opening. 

2. Gates shall be bonded to the grounding conductor, jumper, or fence. 

3. A buried bonding jumper shall be used to bond across a gate or other opening in the fence, unless 
a nonconducting fence section is used. 

4. If barbed wire strands are used above the fence fabric, the barbed wire strands shall be bonded to 
the grounding conductor, jumper, or fence. 

5. When fence posts are of conducting material, the grounding conductor shall be connected to the 
fence post or posts, as required, with suitable connecting means. 

6 . When fence posts are of nonconducting material , suitable bonding connection shall be made to the 
fence mesh strands and the barbed wire strands at each grounding conductor point. 

093. Grounding Conductor and Means of Connection 

A. Composition of Grounding Conductors 

In all cases, the grounding conductor shall be made of copper or other metals or combinations of 
metals that will not corrode excessively during the expected service life under the existing conditions 
and, if practical, shall be without joint or splice. If joints are unavoidable, they shall be so made and 
maintained as to not materially increase the resistance of the grounding conductor and shall have 
appropriate mechanical and corrosion-resistant characteristics. For surge arresters and ground 
detectors, the grounding conductor or conductors shall be as short, straight, and free from sharp bends 
as practical. Metallic electrical equipment cases or the structural metal frame of a building or structure 
may serve as part of a grounding conductor to an acceptable grounding electrode. 

In no case shall a circuit-opening device be inserted in the grounding conductor or connection ex- 
cept where its operation will result in the automatic disconnection from all sources of energy of the 
circuit leads connected to the equipment so grounded. 

EXCEPTION 1: For dc systems over 750 V, grounding conductor circuit-opening devices shall be permitted for 
changing between a remote electrode and a local ground through surge arresters. 

EXCEPTION 2: Temporary disconnection of grounding conductors for testing purposes, under competent super- 
vision, shall be permitted. 

EXCEPTION 3: Disconnection of a grounding conductor from a surge arrester is allowed when accomplished by 
means of a surge-arrester disconnector. 

NOTE: The base of the surge arrester may remain at line potential following operation of the disconnector. 

— IZJ 



The numbers in brackets correspond to those bibliographical items listed in Appendix B. 

Copyright © 2001 IEEE. All rights reserved. 



093B SECTION 9. GROUNDING METHODS 093C6 



B. Connection of Grounding Conductors 

Connection of the grounding conductor shall be made by a means matching the characteristics of both 
the grounded and grounding conductors, and shall be suitable for the environmental exposure. These 
means include brazing, welding, mechanical and compression connections, ground clamps, and 
ground straps. Soldering is acceptable only in conjunction with lead sheaths. 

C. Ampacity and Strength 

For bare grounding conductors, the short time ampacity is the current that the conductor can carry for 
the time during which the current flows without melting or affecting the design characteristics of the 
conductor. For insulated grounding conductors, the short time ampacity is the current that the conduc- 
tor can carry for the applicable time without affecting the design characteristics of the insulation. 
Where grounding conductors at one location are paralleled, the increased total current capacity may 
be considered. 

1 . System Grounding Conductors for Single-Grounded Systems 

The system grounding conductor or conductors for a system with single-system grounding 
electrode or set of electrodes, exclusive of grounds at individual services, shall have a short time 
ampacity adequate for the fault current that can flow in the grounding conductors for the operating 
time of the system-protective device. If this value cannot be readily determined, continuous 
ampacity of the grounding conductor or conductors shall be not less than the full-load continuous 
current of the system supply transformer or other source of supply. 

2. System Grounding Conductors for Multi-Grounded Alternating Current Systems 

The system grounding conductors for an ac system with grounds at more than one location exclu- 
sive of grounds at individual services shall have continuous total ampacities at each location of 
not less than one-fifth that of the conductors to which they are attached. (See also Rule 093C8.) 

3 . Grounding Conductors for Instrument Transformers 

The grounding conductor for instrument cases and secondary circuits for instrument transformers 
shall not be smaller than AWG No. 12 copper or shall have equivalent short time ampacity. 

4. Grounding Conductors for Primary Surge Arresters 

The grounding conductor or conductors shall have adequate short time ampacity under conditions 
of excess current caused by or following a surge. Individual arrester grounding conductors shall 
be no smaller than AWG No. 6 copper or AWG No. 4 aluminum. 

EXCEPTION: Arrester grounding conductors may be copper-clad or aluminum-clad steel wire having not 
less than 30% of the conductivity of solid copper or aluminum wire of the same diameter, respectively. 

Where flexibility of the grounding conductor, such as adjacent to the base of the arrester, is 
vital to its proper operation, a suitably flexible conductor shall be employed. 

5 . Grounding Conductors for Equipment , Messenger Wires , and Guys 

a. Conductors 

The grounding conductors for equipment, raceways, cable, messenger wires, guys, sheaths, 
and other metal enclosures for wires shall have short time ampacities adequate for the avail- 
able fault current and operating time of the system fault-protective device. If no overcurrent 
or fault protection is provided, the ampacity of the grounding conductor shall be determined 
by the design and operating conditions of the circuit, but shall be not less than that of AWG 
No. 8 copper. Where the adequacy and continuity of the conductor enclosures and their attach- 
ment to the equipment enclosures is assured, this path can constitute the equipment grounding 
conductor. 

b. Connections 

Connections of the grounding conductor shall be to a suitable lug, terminal, or device not dis- 
turbed in normal inspection, maintenance, or operation. 

6. Fences 

The grounding conductor for fences required to be grounded by other parts of this code shall meet 
the requirements of Rule 093C5 or shall be steel wire not smaller than Stl WG No. 5. 

19 
Copyright © 2001 IEEE. All rights reserved. 



093C7 SECTION 9. GROUNDING METHODS 093E5 



7. Bonding of Equipment Frames and Enclosures 

Where required, a low-impedance metallic path shall be provided to conduct fault current back to 
the grounded terminal of the local supply. Where the supply is remote, the metallic path shall 
interconnect the equipment frames and enclosures with all other nonenergized conducting 
components within reach and shall additionally be connected to ground as outlined in Rule 093C5. 
Short time ampacities of bonding conductors shall be adequate for the duty involved. 

8. Ampacity Limit 

No grounding conductor need have greater ampacity than either: 

a. The phase conductors that would supply the ground fault current, or 

b. The maximum current that can flow through it to the ground electrode or electrodes to which 
it is attached. For a single grounding conductor and connected electrode or electrodes, this 
would be the supply voltage divided by the electrode resistance (approximately). 

9. Strength 

All grounding conductors shall have mechanical strength suitable for the conditions to which they 
may reasonably be subjected. 

Furthermore, unguarded grounding conductors shall have a tensile strength not less than that 
of AWG No. 8 soft-drawn copper, except as noted in Rule 093C3. 

D. Guarding and Protection 

1 . The grounding conductors for single-grounded systems and those exposed to mechanical damage 
shall be guarded. However, grounding conductors need not be guarded where not readily accessi- 
ble to the public nor where grounding multi-grounded circuits or equipment. 

2. Where guarding is required, grounding conductors shall be protected by guards suitable for the 
exposure to which they may reasonably be subjected. The guards should extend for not less than 
2.45 m (8 ft) above the ground or platform from which the grounding conductors are accessible to 
the public. 

3 . Where guarding is not required , grounds shall be protected by being substantially attached closely 
to the surface of the pole or other structure in areas of exposure to mechanical damage and, where 
practical, on the portion of the structure having least exposure. 

4. Guards used for grounding conductors of lightning-protection equipment shall be of nonmetallic 
materials if the guard completely encloses the grounding conductor or is not bonded at both ends 
to the grounding conductor. 

E. Underground 

1. Grounding conductors laid directly underground shall be laid slack or shall be of sufficient 
strength to allow for earth movement or settling that is normal at the particular location. 

2. Direct-buried uninsulated joints or splices in grounding conductors shall be made with methods 
suitable for the application and shall have appropriate corrosion resistance, required permanence, 
appropriate mechanical characteristics, and required ampacity. The number of joints or splices 
should be the minimum practical. 

3. Grounding cable insulation shielding systems shall be interconnected with all other accessible 
grounded power supply equipment in manholes, handholes, and vaults. 

EXCEPTION: Where cathodic protection or shield cross-bonding is involved, interconnection may be 
omitted. 

4. Looped magnetic elements such as structural steel, piping, reinforcing bars, etc., should not sep- 
arate grounding conductors from the phase conductors of circuits they serve. 

5. Metals used for grounding, in direct contact with earth, concrete, or masonry, shall have been 
proven suitable for such exposure. 

NOTE 1: Under present technology, aluminum has not generally been proven suitable for such use. 

NOTE 2: Metals of different galvanic potentials that are electrically interconnected may require protection 
against galvanic corrosion. 

20 
Copyright © 2001 IEEE. All rights reserved. 



093E6 SECTION 9. GROUNDING METHODS 094B ! 



6. Sheath Transposition Connections (Cross-Bonding) 

a. Where cable insulating shields or sheaths, which are normally connected to ground, are 
insulated from ground to minimize shield circulating currents, they shall be insulated from 
personnel contact at accessible locations. Transposition connections and bonding jumpers 
shall be insulated for nominal 600 V service, unless the normal shielding voltage exceeds this 
level, in which case the insulation shall be ample for the working voltage to ground. 

b. Bonding jumpers and connecting means shall be sized and selected to carry the available fault 
current without damaging jumper insulation or sheath connections. 

F. Common Grounding Conductor for Circuits, Metal Raceways, and Equipment 

Where the ampacity of a supply system grounding conductor is also adequate for equipment 
grounding requirements, this conductor may be used for the combined purpose. Equipment referred 
to includes the frames and enclosures of supply system control and auxiliary components, conductor 
raceways, cable shields, and other enclosures. 

094. Grounding Electrodes 

The grounding electrode shall be permanent and adequate for the electrical system involved. A 
common electrode or electrode system shall be employed for grounding the electrical system and the 
conductor enclosures and equipment served by that system. This may be accomplished by 
interconnecting these elements at the point of connection of grounding conductor, Rule 092. 
Grounding electrodes shall be one of the following: 

A. Existing Electrodes 

Existing electrodes consist of conducting items installed for purposes other than grounding: 

1 . Metallic Water Piping System 

Extensive metallic underground cold water piping systems may be used as grounding electrodes. 
NOTE: Such systems normally have very low resistance to earth and have been extensively used in the past. 
They are the preferred electrode type where they are readily accessible. 

EXCEPTION: Water systems with nonmetallic , non-current-carrying pipe or insulating joints are not suitable 
for use as grounding electrodes. 

2. Local Systems 

Isolated buried metallic cold water piping connecting to wells having sufficiently low measured 
resistance to earth may be used as grounding electrodes. 

NOTE: Care should be exercised to ensure that all parts that might become disconnected are effectively bond- 
ed together. 

3 . Steel Reinforcing Bars in Concrete Foundations and Footings 

The reinforcing bar system of a concrete foundation or footing that is not insulated from direct 
contact with earth, and that extends at least 900 mm (3 ft) below grade, constitutes an effective 
and acceptable type of grounding electrode. Where steel supported on this foundation is to be used 
as a grounding conductor (tower, structure, etc.), it shall be interconnected by bonding between 
anchor bolts and reinforcing bars or by cable from the reinforcing bars to the structure above the 
concrete. 

The normally applied steel ties are considered to provide adequate bonding between bars of 
the reinforcing cage. 

NOTE: Where reinforcing bars in concrete are not suitably connected to a metal structure above the concrete, 
and the latter structure is subjected to grounding discharge currents (even connected to another electrode), 
there is likelihood of damage to the intervening concrete from ground-seeking current passing through the 
semiconducting concrete. 

B. Made Electrodes 
1 . General 

Where made electrodes are used, they shall, as far as practical, penetrate permanent moisture level 
and below the frostline. Made electrodes shall be of metal or combinations of metals that do not 
corrode excessively under the existing conditions for the expected service life. 

21 
Copyright © 2001 IEEE. All rights reserved. 



I 



094B 1 SECTION 9. GROUNDING METHODS 094B4b 



All outer surfaces of made electrodes shall be conductive, that is, not having paint, enamel, or 
other covering of an insulating type. 

2. Driven Rods 

a. Driven rods may be sectional; the total length shall be not less than 2 .45 m (8 ft) . Iron or steel rods 
shall have across-sectional dimension of not less than 1 5 mm (5/8 in) . Copper-clad , stainless steel , 
or stainless steel-clad rods shall have a cross-sectional dimension of not less than 1 2 mm (1/2 in) . 

b. Longer rods or multiple rods may be used to reduce the ground resistance. Spacing between 

multiple rods should be not less than 1 .8 m (6 ft). 

EXCEPTION: Other dimensions or configurations may be used if their suitability is supported by a qual- 
ified engineering study. 

c. Driven depth shall be not less than 2.45 m (8 ft). The upper end shall be flush with or below 
the ground level unless suitably protected. 

EXCEPTION 1: Where rock bottom is encountered, driven depth may be less than 2.45 m (8 ft), or other 
types of electrode may be employed. 

EXCEPTION 2: When contained within pad-mounted equipment, vaults, manholes, or similar enclo- 
sures, the driven depth may be reduced to 2.3 m (7.5 ft). 

3 . Buried Wire , Strips , or Plates 

In areas of high soil resistivity or shallow bedrock, or where lower resistance is required than at- 
tainable with driven rods, one or more of the following electrodes may be more useful: 

a. Wire 

Bare wires 4 mm (0.162 in) in diameter or larger, conforming to Rule 093E5, buried in earth 
at a depth not less than 450 mm (18 in) and not less than 30 m (100 ft) total in length, laid 
approximately straight, constitute an acceptably made electrode. (This is frequently designat- 
ed a counterpoise.) The wire may be in a single length or may be several lengths connected at 
ends or at some point away from the ends. The wire may take the form of a network with many 
parallel wires spaced in two-dimensional array, referred to as a grid. 
EXCEPTION 1 : Where rock bottom is encountered, burial depth may be less than 450 mm (18 in). 
EXCEPTION 2: Other lengths or configurations may be used if their suitability is supported by a quali- 
fied engineering study. 

b. Strips 

Strips of metal not less than 3 .0 m ( 10 ft) in total length and with total (two sides) surface not 
less than 0.47 m 2 (5 ft 2 ) buried in soil at a depth not less than 450 mm (18 in) constitute an 
acceptably made electrode. Ferrous metal electrodes shall be not less than 6 mm (0.25 in) in 
thickness and nonferrous metal electrodes not less than 1 .5 mm (0.06 in). 
NOTE: Strip electrodes are frequently useful in rocky areas where only irregularly shaped pits are prac- 
tical to excavate. 

c. Plates or Sheets 

Metal plates or sheets having not less than 0.185 m 2 (2 ft 2 ) of surface exposed to the soil, and 
at a depth of not less than 1 .5 m (5 ft), constitute an acceptable made electrode. Ferrous metal 
electrodes shall be not less than 6 mm (0.25 in) in thickness and nonferrous metal electrodes 
not less than 1 .5 mm (0.06 in). 

4. Pole-Butt Plates and Wire Wraps 

a. General 

In areas of very low soil resistivity there are two constructions, described in specifications b 
and c below, that may provide effective grounding electrode functions although they are inad- 
equate in most other locations. Where these have been proven to have adequately low earth 
resistance by the application of Rule 96, two such electrodes may be counted as one made elec- 
trode and ground for application of Rules 92Cla, 92C2b, 96C, and 97C; however, these types 
shall not be the sole grounding electrode at transformer locations. 

b. Pole-Butt Plates 

Subject to the limitations of Rule 94B4a, a pole-butt plate on the base of a wooden pole, pos- 
sibly folded up around the base of the pole butt, may be considered an acceptable electrode in 
locations where the limitations of Rule 96 are met. The plates shall be not less than 6 mm 
(1/4 in) thick if of ferrous metal and not less than 1 .5 mm (0.06 in) thick if of nonferrous metal. 
Further, the plate area exposed to the soil shall be not less than 0.046 m 2 (0.5 ft 2 ). 

22 
Copyright © 2001 IEEE. All rights reserved. 



094B4c SECTION 9. GROUNDING METHODS 095A4 



c. Wire Wrap 

Subject to the limitations of Rule 94B4a, made electrodes may be wire attached to the pole 
previous to the setting of the pole. The wire shall be of copper or other metals that will not 
corrode excessively under the existing conditions and shall have a continuous bare or exposed 
length below ground level of not less than 3 .7 m ( 1 2 ft) , shall extend to the bottom of the pole , 
and shall not be smaller than AWG No. 6. 

5. Concentric Neutral Cable 

Systems employing extensive [30 m (100 ft) minimum length] buried bare concentric neutral 
cable in contact with the earth may employ the concentric neutral as a grounding electrode. The 
concentric neutral may be covered with a semi-conducting jacket that has a radial resistivity not 
exceeding 100 mQ and that will remain essentially stable in service. The radial resistivity of the 
jacket material is that value calculated from measurements on a unit length of cable, of the 
resistance between the concentric neutral and a surrounding conducting medium. Radial 
resistivity equals resistance of unit length times the surface area of jacket divided by the average 
thickness of the jacket over the neutral conductors. All dimensions are to be expressed in meters. 

6. Concrete-Encased Electrodes 

A metallic wire, rod, or structural shape, meeting Rule 093E5 and encased in concrete, that is not 
insulated from direct contact with earth, shall constitute an acceptable ground electrode. The con- 
crete depth below grade shall be not less than 300 mm (1 ft), and a depth of 750 mm (2.5 ft) is 
recommended. Wire shall be no smaller than AWG No. 4 if copper, or 9 mm (3/8 in) diameter or 
AWG No. 1/0 if steel. It shall be not less than 6.1 m (20 ft) long, and shall remain entirely within 
the concrete except for the external connection. The conductor should be run as straight as 
practical. 

The metal elements may be composed of a number of shorter lengths arrayed within the con- 
crete and connected together (for example, the reinforcing system in a structural footing). 
EXCEPTION: Other wire length or configurations may be used if their suitability is supported by a qualified 
engineering study. 

NOTE 1: The lowest resistance per unit wire length will result from a straight wire installation. 
NOTE 2: The outline of the concrete need not be regular, but may conform to an irregular or rocky 
excavation. 

NOTE 3: Concrete-encased electrodes are frequently more practical or effective than driven rods or strips or 
plates buried directly in earth. 

095. Method of Connection to Electrode 

A. Ground Connections 

The grounding connection shall be as accessible as practical and shall be made to the electrode by 
methods that provide the required permanence, appropriate mechanical characteristics, corrosion re- 
sistance, and required ampacity such as: 

1 . An effective clamp, fitting, braze, or weld. 

2. A bronze plug that has been tightly screwed into the electrode. 

3. For steel-framed structures, employing a concrete-encased reinforcing bar electrode, a steel rod 
similar to the reinforcing bar shall be used to join, by welding, a main vertical reinforcing bar to 
an anchor bolt. The bolt shall be substantially connected to the baseplate of the steel column 
supported on that footing. The electrical system may then be connected (for grounding) to the 
building frame by welding or by a bronze bolt tapped into a structural member of that frame. 

4. For nonsteel frame structures employing a concrete-encased rod or wire electrode, an insulated 
copper conductor of size meeting the requirements of Rule 093C (except not smaller than AWG 
No. 4) shall be connected to the steel rod or wire using a cable clamp suitable for steel cable. This 
clamp and all the bared portion of the copper conductor, including ends of exposed strands within 
the concrete, shall be completely covered with mastic or sealing compound before concrete is 
poured. The copper conductor end shall be brought to or out of the concrete surface at the required 
location for connection to the electrical system. If the copper wire is carried beyond the surface of 
the concrete, it shall be no smaller than AWG No. 2. 

23 
Copyright © 2001 IEEE. All rights reserved. 



I 



095B SECTION 9. GROUNDING METHODS 096C 



Alternately, the copper wire may be brought out of the concrete at the bottom of the hole and 
carried external to the concrete for surface connection. 

B. Point of Connection to Piping Systems 

1 . The point of connection of a grounding conductor to a metallic water piping system shall be as 
near as is practical to the water-service entrance to the building or near the equipment to be 
grounded and shall be accessible. If a water meter is between the point of connection and the un- 
derground water pipe, the metallic water piping system shall be made electrically continuous by 
bonding together all parts between the connection and the pipe entrance that may become discon- 
nected, such as meters and service unions. 

2 . Made grounds or grounded structures should be separated by 3 .0 m ( 1 ft) or more from pipelines 
used for the transmission of flammable liquids or gases operating at high pressure [1030 kPa 
(150 lb/in 2 ) or greater] unless they are electrically interconnected and cathodically protected as a 
single unit. Grounds within 3.0 m (10 ft) of such pipelines should be avoided or shall be coordi- 
nated so that hazardous ac conditions will not exist and cathodic protection of the pipeline will not 
be nullified. 

RECOMMENDATION: It is recommended that calculations or tests be used to determine the required 
separation of ground electrodes for high-voltage direct-current (HVDC) systems from flammable liquid or 
high-pressure gas pipelines. 
NOTE: Ground electrodes for HVDC systems over 750 V may require greater separation. 

C. Contact Surfaces 

If any coating of nonconducting material, such as enamel, rust, or scale, is present on electrode contact 
surfaces at the point of connection, such a coating shall be thoroughly removed where required to 
obtain the requisite good connection. Special fittings so designed as to make such removal of 
nonconducting coatings unnecessary may also be used. 

096. Ground Resistance Requirements 

Grounding systems shall be designed to minimize hazard to personnel and shall have resistances to 
ground low enough to permit prompt operation of circuit protective devices. Grounding systems may 
consist of buried conductors and grounding electrodes. 

A. Supply Stations 

Supply stations may require extensive grounding systems consisting of multiple buried conductors, 
grounding electrodes, or interconnected combinations of both. Grounding systems shall be designed 
to limit touch, step, mesh, and transferred potentials in accordance with industry practices. 
NOTE: IEEE Std 80-2000 [B21] is one source that may be utilized to provide guidance in meeting these 
requirements. 

B. Single-Grounded (Unigrounded or Delta) Systems 

Individual made electrodes shall, where practical, have a resistance to ground not exceeding 25 Q. If 
a single electrode resistance exceeds 25 Q, two electrodes connected in parallel shall be used. 

C. Multi-Grounded Systems 

The neutral, which shall be of sufficient size and ampacity for the duty involved, shall be connected 

to a made or existing electrode at each transformer location and at a sufficient number of additional 

points with made or existing electrodes to total not less than four grounds in each 1 .6 km (1 mi) of the 

entire line, not including grounds at individual services. 

EXCEPTION: Where underwater crossings are encountered, the requirement of made electrodes to total not less 

than four grounds in each 1 .6 km (1 mi) of the entire line does not apply for the underwater portion if the neutral 

is of sufficient size and capacity for the duty involved and the requirements of Rule 092B2 are met. 

NOTE: Multi-grounded systems extending over a substantial distance are more dependent on the multiplicity of 

grounding electrodes than on the resistance to ground of any individual electrode. Therefore, no specific values 

are imposed for the resistance of individual electrodes. 

RECOMMENDATION: This rule may be applied to shield wire(s) grounded at the source and which meet the 

multigrounding requirements of this rule. 

24 
Copyright © 2001 IEEE. All rights reserved. 



°97 SECTION 9. GROUNDING METHODS 097F 



097. Separation of Grounding Conductors 

A. Except as permitted in Rule 097B, grounding conductors from equipment and circuits of each of the 
following classes shall be run separately to the grounding electrode for each of the following classes: 

1 . Surge arresters of circuits over 750 V and frames of any equipment operating at over 750 V. 

2. Lighting and power circuits under 750 V. 

3 . Shield wires of power circuits. 

4. Lightning rods, unless attached to a grounded metal supporting structure. 

Alternatively, the grounding conductors shall be run separately to a sufficiently heavy ground bus 
or system ground cable that is well connected to ground at more than one place. 

B. The grounding conductors of the equipment classes detailed in Rules 097A1 , 097 A2, and 097 A3 may 
be interconnected utilizing a single grounding conductor, provided: 

1 . There is a direct-earth grounding connection at each surge-arrester location, and 

2. The secondary neutral or the grounded secondary phase conductor is common with or connected 
| to a primary neutral or a shield wire meeting the grounding requirements of Rule 097C. 

C. Primary and secondary circuits utilizing a single conductor as a common neutral shall have at least 
four ground connections on such conductor in each 1 .6 km (1 mi) of line, exclusive of ground con- 
nections at customers' service equipment. 

D. Ungrounded or Single-Grounded Systems and Multi-Grounded Systems 

1 . Ungrounded or Single-Grounded Systems 

Where the secondary neutral is not interconnected with the primary surge-arrester grounding 
conductor as in Rule 097B, interconnection may be made through a spark gap or device that 
performs an equivalent function. The gap or device shall have a 60 Hz breakdown voltage of at 
least twice the primary circuit voltage but not necessarily more than 10 kV. At least one other 
grounding connection on the secondary neutral shall be provided with its grounding electrode 
located at a distance of not less than 6.1m (20 ft) from the surge-arrester grounding electrode in 
addition to customer's grounds at each service entrance. The primary grounding conductor, or the 
secondary grounding conductor, shall be insulated for 600 V. 

2. Multi-Grounded Systems 
On multi-grounded systems, the primary and secondary neutrals should be interconnected accord- 
ing to Rule 097B. However, where it is necessary to separate the neutrals, interconnection of the 
neutrals shall be made through a spark gap or a device that performs an equivalent function. The 
gap or device shall have a 60 Hz breakdown voltage not exceeding 3 kV. At least one other 
grounding connection on the secondary neutral shall be provided with its grounding electrode lo- 
cated at a distance not less than 1 .80 m (6 ft) from the primary neutral and surge-arrester grounding 
electrode in addition to the customer's grounds at each service entrance .Where the primary and 
secondary neutrals are not directly interconnected, the primary grounding conductor, or the sec- 
ondary grounding conductor, or both, shall be insulated for 600 V. 

NOTE 1: A difference of voltage can exist where primary and secondary neutrals are not directly 
interconnected. For example, where metallic equipment is bonded to the secondary grounding conductor and 
is installed on the same pole, the primary grounding conductor would be insulated. 

NOTE 2: Cooperation of all communications and supply utilities, customers of these utilities, and others may 
be necessary to obtain effective isolation between primary and secondary neutrals. 

E. Where separate electrodes are used for system isolation, separate grounding conductors shall be used. 
Where multiple electrodes are used to reduce grounding resistance, they may be bonded together and 
connected to a single grounding conductor. 

F. Made electrodes used for grounding surge arresters of ungrounded supply systems operated at 
potentials exceeding 15 kV phase to phase should be located at least 6.1 m (20 ft) from buried 
communication cables. Where lines with lesser separations are to be constructed, reasonable advance 
notice should be given to the owners or operators of the affected systems. 

25 
Copyright © 2001 IEEE. All rights reserved. 



tcM 



097G SECTION 9. GROUNDING METHODS 099C 



G. Communication Systems 

Where both electric supply systems and communication systems are grounded on a joint use structure, 
either a single grounding conductor should be used for both systems or the electric supply and 
communication grounding conductors should be bonded together, except where separation is required 
by Rule 097 A. Where the electric supply utility is maintaining isolation between primary and 
secondary neutrals, the communication system ground shall be connected only to the primary 
grounding conductor. 

098. Number 098 not used in this edition. 

099. Additional Requirements for Communication Apparatus 

Where required to be grounded by other parts of this code, communication apparatus shall be ground- 
ed in the following manner. 
See NOTE 2 in Rule 097D2. 

A. Electrode 

The grounding conductor shall be connected to an acceptable grounding electrode as follows: 

1 . Where available and where the supply service is grounded to an acceptable electrode, as described 
in Rule 094, to the grounded metallic supply service conduit, service equipment enclosure, 
grounding electrode conductors, or grounding electrode conductors' metal enclosure. 

2. Where the grounding means of Rule 099A1 is not available, to a grounding electrode as described 
in Rule 094 A. 

3 . Where the grounding means of Rule 099 A 1 or 099 A2 are not available, to a grounding electrode 
as described in Rule 094B. 

EXCEPTION: A variance to Rule 094B2 is allowed for this application. Iron or steel rods may have a cross- 
sectional dimension of not less than 13 mm (.50 in) and a length of not less than 1 .50 m (5 ft). The driven 
depth shall be 1 .50 m (5 ft), subject to EXCEPTION 1 of Rule 094B2. 

B. Electrode Connection 

The grounding conductor shall preferably be made of copper (or other material that will not corrode 
excessively under the prevailing conditions of use) and shall be not less than AWG No. 14 in size. The 
grounding conductor shall be attached to the electrode by means of a bolted clamp or other suitable 
methods. 

C. Bonding of Electrodes 

A bond not smaller than AWG No. 6 copper or equivalent shall be placed between the communication 

grounding electrode and the supply system neutral grounding electrode where separate electrodes are 

used in or on the same building or structure being served. 

RECOMMENDATION: If water piping is used as a bonding means, care must be taken to assure that the metallic 

path is continuous between electrodes. 

NOTE: See NEC Article 800-40(d) for corresponding NEC requirements. 



26 
Copyright © 2001 IEEE. All rights reserved. 



100 PARTI. ELECTRIC SUPPLY STATIONS 101 

Part 1. 

Rules for the Installation 

and Maintenance of Electric 

Supply Stations and Equipment 

Section 10. 
Purpose and Scope of Rules 



100. Purpose 

The purpose of Part 1 of this code is the practical safeguarding of persons during the installation, op- 
eration, or maintenance of electric supply stations and their associated equipment. 

101. Scope 

Part 1 of this code covers the electric supply conductors and equipment, along with the associated 
structural arrangements in electric supply stations, that are accessible only to qualified personnel. It 
also covers the conductors and equipment employed primarily for the utilization of electric power 
when such conductors and equipment are used by the utility in the exercise of its function as a utility. 



1 



27 
Copyright © 2001 IEEE. All rights reserved. 



1 10 PART 1 . ELECTRIC SUPPLY STATIONS 1 10B2 

Section 11. 
Protective Arrangements in Electric Supply Stations 

110. General Requirements 

A. Enclosure of Equipment 

1 . Types of Enclosures 

Rooms and spaces in which electric supply conductors or equipment are installed shall be so ar- 
ranged with fences, screens, partitions, or walls to form an enclosure as to limit the likelihood of 
entrance of unauthorized persons or interference by them with equipment inside. Entrances not 
under observation of an authorized attendant shall be kept locked. 

A safety sign shall be displayed at each entrances. For fenced electric supply stations, a safety 
sign shall be displayed on each side. 

NOTE: ANSI Z535.1-1998, ANSI Z535.2-1998, ANSI Z535.3-1998, ANSI Z535.4-1998, and ANSI 
Z535 .5-1998 contain information regarding safety signs. 

Metal fences, when used to enclose electric supply stations having energized electric conduc- 
tors or equipment, shall have a height not less than 2.13 m (7 ft) overall and shall be grounded in 
accordance with Section 9. 

The requirements for fence height may be satisfied with any one of the following: 

a. Fence fabric, 2.13 m (7 ft) or more in height. 

b . A combination of 1 .80 m (6 ft) or more of fence fabric and an extension utilizing three or more 
strands of barbed wire to achieve an overall height of the fence of not less than 2.13 m (7 ft). 

c. Other types of construction, such as nonmetallic material, that present equivalent barriers to 
climbing or other unauthorized entry. 

2. Safety Clearance Zone 

Fences or walls, when installed as barriers for unauthorized personnel, shall be located such that 
exposed live parts are outside the safety clearance zone as illustrated in Figure 1 10-1 and shown 
in Table 110-1. 

EXCEPTION 1 : Where a fence, partition, or wall with no openings through which sticks or other objects can 
be inserted is utilized, live parts complying with the requirements of this code may be installed within the 
safety clearance zone if they are below the horizontal line projected from the top of the fence or wall. 
EXCEPTION 2: The safety clearance zone requirement is not applicable to internal fences within an electric 
supply station perimeter fence. 

B. Rooms and Spaces 

All rooms and spaces in which electric supply equipment is installed shall comply with the following 
requirements: 

1 . Construction 

They shall be as much as practical noncombustible. 

NOTE: This rule is not intended to prevent wood poles from being used to support conductors or equipment 

in electric supply stations. 

2. Use 

They should be as much as practical free from combustible materials, dust, and fumes and shall 
not be used for manufacturing or for storage. 

EXCEPTION 1: Equipment or material essential for maintenance of the installed equipment may be stored 
if guarded or separated from live parts as required by Rule 124. 

EXCEPTION 2: Materials related to station, transmission, or distribution construction or maintenance work 
may be stored in the station if located in an area separated from the station electric supply equipment by a 
fence meeting the requirements of Rule 110A. 

EXCEPTION 3: Stored material related to station, transmission, and distribution construction and 
maintenance work in progress may be temporarily located in a storage space meeting all of the following 
requirements: 

(1) Guarded or separated from live parts as required by Rule 124. 

(2) Station exits continue to meet the requirements of Rule 113. 

(3) Station working space continues to meet the requirements of Rule 125. 

28 
Copyright © 2001 IEEE. All rights reserved. 



F-110-1 



PART 1 . ELECTRIC SUPPLY STATIONS 



T-110-1 



/ 



/ 




J. 



//////////////////////// 



K 



Fig 110-1 
Safety Clearance to Electric Supply Station Fences 





Table 110-1 
Values for Use with Fig 110-1 




Nominal Voltage 
Between Phases 


Typical BIL 


Dimension "R" 


m 


■;. 


151-7200 


95 


3.0 


10.0 

!0 J 
10.3 
10.6 

km; 


13 800 


110 


3.1 


23 000 


150 


3.1 


34 500 


200 


3.2 


46 000 


250 


3.3 


69 000 


350 


3.5 


J 1.6 


115 000 


550 


4.0 


13.0 
13~7 
14.-, 

14.9 
15.4 


138 000 


650 


4.2 


161 000 


750 


4.4 


230 000 


825 


4.5 


230 000 


900 


4.7 


345 000 


1050 


5.0 


16.4 
I/.3 
1 S 3 
: 19.8 
21.5 


345 000 


1175 


5.3 


345 000 


1300 


5.5 


500 000 


1550 


6.0 


500 000 


1800 


6.6 


765 000 


2050 


7.1 


.-.;■:: 23.4.; : . 



29 
Copyright © 2001 IEEE. All rights reserved. 



1 10B2 PART 1 . ELECTRIC SUPPLY STATIONS 1 1 IE 



(4) Access is limited to qualified personnel. 

(5) The storage location and content is such that the risk of fire does not unreasonably jeopardize station 
operation. 

(For battery areas, see Section 14; for guarding, see Rule 124; for auxiliary equipment in classified locations, 
see Rule 127.) 

3. Ventilation 

There should be sufficient ventilation to maintain operating temperatures within ratings, arranged 
to minimize accumulation of airborne contaminants under any operating conditions. 

4. Moisture and Weather 

They should be dry. In outdoor stations or stations in wet tunnels, subways or other moist or high- 
humidity locations, the equipment shall be suitably designed to withstand the prevailing 
atmospheric conditions. 

C. Electric Equipment 

All stationary equipment shall be supported and secured in a manner consistent with reasonably ex- 
pected conditions of service. Consideration shall be given to the fact that certain heavy equipment, 
such as transformers, can be secured in place by their weight. However, equipment that generates dy- 
namic forces during operation may require appropriate additional measures. 

111. Illumination 

A. Under Normal Conditions 

Rooms and spaces shall have means for artificial illumination. Illumination levels not less than those 
listed in Table 111-1 are recommended for safety to be maintained on the task. 

B. Emergency Lighting 

1 . A separate emergency source of illumination with automatic initiation, from an independent gen- 
erator, storage battery, or other suitable source, shall be provided in every attended station. 

2. Emergency lighting of 1 1 lux (1 footcandle) shall be provided in exit paths from all areas of at- 
tended stations . Consideration must be given to the type of service to be rendered, whether of short 
or long duration. The minimum duration shall be 1-1/2 h. It is recommended that emergency cir- 
cuit wiring shall be kept independent of all other wiring and equipment. 

C. Fixtures 

Arrangements for permanent fixtures and plug receptacles shall be such that portable cords need not 
be brought into dangerous proximity to live or moving parts. All lighting shall be controlled and ser- 
viced from safely accessible locations. 

D. Attachment Plugs and Receptacles for General Use 

Portable conductors shall be attached to fixed wiring only through separable attachment plugs that 
will disconnect all poles by one operation. Receptacles installed on two- or three- wire single-phase, 
ac branch circuits shall be of the grounding type. Receptacles connected to circuits having different 
voltages, frequencies, or types of current (ac or dc) on the same premises shall be of such design that 
attachment plugs used on such circuits are not interchangeable. 

E. Receptacles in Damp or Wet Locations 

All 120 V ac permanent receptacles shall either be provided with ground-fault interrupter (GFI) pro- 
tection or be on a grounded circuit that is tested at such intervals as experience has shown to be 
necessary. 

30 
Copyright © 2001 IEEE. All rights reserved. 



T-lll-1 



PART 1 . ELECTRIC SUPPLY STATIONS 



T-lll-1 



Table 111-1 
Illumination Levels 



Location 


lux 


footcandlts 


Generating Station 






Air-conditioning equipment, air preheater and fan floor, ash sluicing 


55 


.:■■■'; 5 ■.'.:: ' 

' '.'■y-iO',': .;■■ 
5 

to 

5 

:.':'■ -25 '■'■.''■' 
;'■■-'■■■ -5 ':.-■- 

5 

25 

15 


Auxiliaries, battery areas, boiler feed pumps, tanks, compressors, 
gage area 


110 


Boiler platforms 


55 


Burner platforms 


110 


Cable room, circulator, or pump bay 


55 


Chemical laboratory 


270 


Coal conveyor, crusher, feeder, scale area, pulverizer, fan area, 
transfer tower 


55 


Condensers, deaerator floor, evaporator floor, heater floors 


55 


Control rooms 
Vertical face of switchboards 
Simplex or section of duplex operator: 




Type A — Large centralized control room 1 .68 m (66 in) above 
floor 


270 


Type B — Ordinary control room 1 .68 m (66 in) above floor 


160 


Section of duplex facing away from operator 


160 


15 
25 

;..:■ 5 ■.:■;■ ' 

'■':■ .-.'5 :■"■'-' '■ 
25 


Bench boards (horizontal level) 


270 


Area inside duplex switchboards 


55 


Rear of all switchboard panels (vertical) 


55 


Dispatch boards 


Horizontal plane (desk level) 


270 


Vertical face of board [1.22 m (48 in) above floor, facing operator]: 


25 

■'.-.; . 10 ■'■. . 


System load dispatch room 


270 


Secondary dispatch room 


160 


Hydrogen and carbon dioxide manifold area 


110 


Precipitators 


55 


5 

.:'.: -.'id '■'■.' ■■ 
'■■■'■■■ , 5 -' "■■'■'■'■ 

5 

10 

10 

:.'. : : : 5: ; . 
10 
:.■;■':. 15 .:.■■:■■ 


Screen house 


110 


Soot or slag blower platform 


55 


Steam headers and throttles 


55 


Switchgear, power 


110 


Telephone equipment room 


110 


Tunnels or galleries, piping 


55 


Turbine bay sub-basement 


110 


Turbine room 


160 


Visitors' gallery 


110 


: ■'■ '"'lO ' ■■■ ;■; 


Water treating area 


110 



I 



31 
Copyright © 2001 IEEE. All rights reserved. 



T-lll-1 



PART 1. ELECTRIC SUPPLY STATIONS 



112B 



Table 111-1 (Continued) 
Illumination Levels 



Location 


lux 


footcandles 


Generating Station (Exterior) 


2 
0.2 

'■".: 0.2 :■: : 

: ". ; 0:5 . 

■■'. C5 

'■': -5 ■. . . : 


Catwalks 


22 


Cinder dumps 


2.2 


Coal-storage area 


2.2 


Coal unloading 


Dock (loading or unloading zone) 


55 


Barge storage area 


5.5 


Car dumper 


5.5 


Tipple 


55 


Conveyers 


22 


Entrances 

Generating or service building 


■ . ;■: : lp;- :■■■ ' 
..'■■ 2 ."."■'■' -' 

■ : : . 10 : '.; : 
'■::■■; :5. ■■■■' ■ 

'.'. ' 0.2; ;.. '■ ■ 

■■■■;. :5.V .. .' 

1 
■:0.2 


Main 


110 


Secondary 


22 


Gate house 


Pedestrian entrance 


110 


Conveyor entrance 


55 


Fence 


2.2 


Fuel-oil delivery headers 


55 


Oil storage tanks 


11 


Open yard 


2.2 


Platforms— boiler, turbine deck 


55 


■ ■.■ ■. : 5 ■■ "■ ■ :■ 


Roadway 


Between or along buildings 


11 


Not bordered by buildings 


5.5 


,-.■.:'■ 0,5 v. : 
~r:\'-% .'>■■' 

■—£... 

■■■■ ■ ■ 2 ■■■ ■■" 

^■■■'■-■"--"^■■^■■■■■i-'V-V-" 


Substation 


General horizontal 


22 


Specific vertical (on disconnects) 


22 



112. Floors , Floor Openings , Passageways , and Stairs 

A. Floors 

Floors shall have even surfaces and afford secure footing. Slippery floors or stairs should be provided 
with antislip covering. 



B. Passageways 

Passageways, including stairways, shall be unobstructed and shall, where practical, provide at least 
2.13 m (7 ft) head room. Where the preceding requirements are not practical, the obstructions should 
be painted, marked, or indicated by safety signs, and the area properly lighted. 

NOTE: ANSI Z535.1-1998, ANSI Z535.2-1998, ANSI Z535.3-1998, ANSI Z535.4-1998, and ANSI Z535.5- 
1998 contain information regarding safety signs. 

32 
Copyright © 2001 IEEE. All rights reserved. 



1 12C PART 1 . ELECTRIC SUPPLY STATIONS 1 14 



C. Railings 

All floor openings without gratings or other adequate cover and raised platforms and walkways in 
excess of 300 mm (1 ft) in height shall be provided with railings. Openings in railings for units such 
as fixed ladders, cranes, and the like shall be provided with adequate guards such as grates, chains, 
or sliding pipe sections. 

D. Stair Guards 

All stairways consisting of four or more risers shall be provided with handrails. 
NOTE: For additional information, see ANSI A1264.1-1995 [B5]. 

E. Top Rails 

All top rails shall be kept unobstructed for a distance of 75 mm (3 in) in all directions except from 
below at supports. 

113. Exits 

A. Clear Exits 

Each room or space and each working space about equipment shall have a means of exit, which shall 
be kept clear of all obstructions. 

B. Double Exits 

If the plan of the room or space and the character and arrangement of equipment are such that an ac- 
cident would be likely to close or make inaccessible a single exit, a second exit shall be provided. 

C. Exit Doors 

Exit doors shall swing out and be equipped with panic bars, pressure plates, or other devices that are 
normally latched but open under simple pressure. 

EXCEPTION: This rule does not apply to exit doors in buildings and rooms containing low-voltage, nonexplo- 
sive equipment, and to gates in fences for outdoor equipment installations. 

114. Fire-Extinguishing Equipment 

Fire-extinguishing equipment approved for the intended use shall be conveniently located and con- 
spicuously marked. 



33 
Copyright © 2001 IEEE. All rights reserved. 



120 PART 1 . ELECTRIC SUPPLY STATIONS 123B 



Section 12. 
Installation and Maintenance of Equipment 

120. General Requirements 

| A. All electric equipment shall be constructed, installed, and maintained so as to safeguard personnel as 
far as practical. 

| B. The rules of this section are applicable to both ac and dc supply stations. 

121. Inspections 

A. In-Service Equipment 

Electric equipment shall be inspected and maintained at such intervals as experience has shown to be 
necessary. Equipment or wiring found to be defective shall be put in good order or permanently dis- 
connected. 

B. Idle Equipment 

Infrequently used equipment or wiring shall be inspected and tested before use to determine its fitness 
for service. Idle equipment energized but not connected to a load shall be inspected and maintained 
at such intervals as experience has shown to be necessary. 

C. Emergency Equipment 

Equipment and wiring maintained for emergency service shall be inspected and tested at such inter- 
vals as experience has shown to be necessary to determine its fitness for service. 

D. New Equipment 

New equipment shall be inspected and tested before being placed in service. New equipment shall be 
tested in accordance with standard industry practices. 

122. Guarding Shaft Ends, Pulleys, Belts, and Suddenly Moving Parts 

A. Mechanical Transmission Machinery 

The methods for safeguarding pulleys, belts, and other equipment used in the mechanical transmis- 
| sion of power shall be in accordance with ANSI/ASME B 1 5 . 1 -2000 . 

B . Suddenly Moving Parts 

Parts of equipment that move suddenly in such a way that persons in the vicinity are likely to be in- 
jured by such movement shall be guarded or isolated. 

123. Protective Grounding 

A. Protective Grounding or Physical Isolation of Non-Current-Carrying Metal Parts 

All electric equipment shall have the exposed non-current-carrying metal parts, such as frames of 
generators and switchboards, cases of transformers, switches, and operating levers, effectively 
grounded or physically isolated. All metallic guards including rails, screen fences, etc., about electric 
equipment shall be effectively grounded. 

B. Grounding Method 

All grounding that is intended to be a permanent and effective protective measure, such as surge- 
arrester grounding, grounding of circuits, equipment, or wire raceways, shall be made in accordance 
with the methods specified in Section 9 of this code. 
NOTE: For additional information, see IEEE Std 80-2000 [B22]. 



34 
Copyright © 2001 IEEE. All rights reserved. 



1 23C PART 1 . ELECTRIC SUPPLY STATIONS 1 24C2 



C. Provision for Grounding Equipment During Maintenance 

Electric equipment or conductors normally operating at more than 600 V between conductors, on or 
about which work is occasionally done while isolated from a source of electric energy by 
disconnecting or isolating switches only, shall be provided with some means for grounding, such as 
switches, connectors, or a readily accessible means for connecting a portable grounding conductor. 
When necessary, grounding may be omitted on conductors normally operating at 25 kV or less and 
not influenced by higher voltage conductors, where visible openings in the source of supply are 
available, and are properly tagged in the open position. (See Part 4 of this code.) 

D. Grounding Methods for Direct-Current Systems over 750 V 

On dc systems greater than 750 V, the dc system shall be grounded in accordance with the methods 
specified in Section 9 of this code. 

124. Guarding Live Parts 

A. Where Required 

1 . Guards shall be provided around all live parts operating above 150 V to ground without an ade- 
quate insulating covering, unless their location gives sufficient horizontal or vertical clearance or 
a combination of these clearances to limit the likelihood of accidental human contact. Clearances 
from live parts to any permanent supporting surface for workers shall equal or exceed either of 
those shown in Table 124-1 and illustrated in Fig 124-1 . 

2. Parts over or near passageways through which material may be carried, or in or near spaces such 
as corridors, storerooms, and boiler rooms used for nonelectrical work, shall be guarded or given 
clearances in excess of those specified such as may be necessary to secure reasonable safety. The 
guards shall be substantial and completely shield or enclose the live parts without openings. In 
spaces used for nonelectrical work, guards should be removable only by means of tools or keys. 

3. Each portion of parts of indeterminate potential, such as telephone wires exposed to induction 
from high- voltage lines, ungrounded neutral connections, ungrounded frames, ungrounded parts 
of insulators or surge arresters, or ungrounded instrument cases connected directly to a high- 
voltage circuit, shall be guarded in accordance with Rule 124A1 on the basis of the maximum 
voltage that may be present on the surface of that portion. The vertical clearance above grade of 
the bottom of such part shall be not less than 2.60 m (8.5 ft) unless it is enclosed or guarded in 
accordance with Rule 124C. 

B. Strength of Guards 

Guards shall be sufficiently strong and shall be supported rigidly and securely enough to limit the 
likelihood of them being displaced or dangerously deflected by a person slipping or falling against 
them. 

C. Types of Guards 

1 . Location or Physical Isolation 

Parts having clearances equal to or greater than specified in Table 124-1 are guarded by location. 
Parts are guarded by isolation when all entrances to enclosed spaces, runways, fixed ladders, and 
the like are kept locked, barricaded, or roped off, and safety signs are posted at all entrances. 
NOTE: ANSI Z535.1-1998, ANSI Z535.2-1998, ANSI Z535.3-1998, ANSI Z535.4-1998, and 
ANSI Z535 .5-1998 contain information regarding safety signs. 

2. Shields or Enclosures 

Guards less than 100 mm (4 in) outside of the guard zone shall completely enclose the parts from 
contact up to the heights listed in column 2 of Table 124-1 . They shall be not closer to the live 
parts than listed in column 4 of Table 124-1 , except when suitable insulating material is used with 
circuits of less than 2500 V to ground. If more than 100 mm (4 in) outside the guard zone, the 
guards shall extend at least 2.60 m (8.5 ft) above the floor. Covers or guards, which must at any 
time be removed while the parts they guard are live, shall be so arranged that they cannot readily 
be brought into contact with live parts. 



35 
Copyright © 2001 IEEE. All rights reserved. 



I 



124C3 



PART 1. ELECTRIC SUPPLY STATIONS 



F-124-1 



3. Supplemental Barriers or Guards Within Electric Supply Stations 

If the vertical distance in Table 124-1 cannot be obtained, railings or fences may be used. Railings 
or fences, if used, shall be not less than 1 .07 m (3.5 ft) high and shall be located at a horizontal 
distance of at least 900 mm (3 ft) [and preferably not more than 1 .20 m (4 ft)] from the nearest 
point of the guard zone that is less than 2.60 m (8.5 ft) above the floor or grade (see Fig 124-2). 

4. Mats 

Mats of rubber or other suitable insulating material complying with ASTM D 178-88 may be used 
at switchboards, switches, or rotating machinery as supplementary protection. 

5. Live Parts Below Supporting Surfaces for Persons 

The supporting surfaces for persons above live parts shall be without openings. Toe boards at 
least 150 mm (6 in) high and handrails shall be provided at all edges. 

6. Insulating Covering on Conductors or Parts 

Conductors and parts may be considered as guarded by insulation if they have either of the 
following: 

a. Insulation covering of a type and thickness suitable for the voltage and conditions under 
which they are expected to be operated, and if operating above 2500 V to ground, having me- 
tallic insulation shielding or semiconducting shield in combination with suitable metallic 
drainage that is grounded to an effective ground. 

EXCEPTION: Nonshielded insulated conductors listed by a qualified testing laboratory shall be permit- 
ted for use up to 8000 V (phase to phase) when the conductors meet the requirements of the NEC, 
Article 310-6. 

b. Barriers or enclosures that are electrically and mechanically suitable for the conditions under 
which they are expected to be operated. 



LIVE PART 



Q 





HORIZONTAL CLEARANCE 
SEE COLUMN 3, TABLE 124-1 



GUARD ZONE AT RADIUS R, SEE 
COLUMN 4, TABLE 124-1 



VERTICAL CLEARANCE 
SEE COLUMN 2, TABLE 124-1 



Fig 124-1 
Clearance From Live Parts 



36 
Copyright © 2001 IEEE. All rights reserved. 



T-124-lA(m) 



PART 1. ELECTRIC SUPPLY STATIONS 



T-124-lA(m) 



m 



Table 124-1 
Clearances From Live Parts 



Part A— Low, Medium, and High Voltages (based on BIL factors) 


Maximum 
Design Voltage 
between Phases 

(1) 


Basic Impulse 

Insulation Level s 

(BIL) 


Vertical clearance of 
unguarded parts 

(2) 1 


Horizontal 

clearance of 

unguarded parts 

(3) 1 


Clearance guard 
to live parts 

(4) 1 


kV 


kV 


m 


m 


mm 


0.151-0.6 


— ■ 


2.64 


1.02 


50 


2.4 


— 


2.67 


1.02 


76 


7.2 


95 


2.69 


1.02 


101 


15 


95 


2.69 


1.02 


101 


15 


110 


2.74 


1.07 


152 


25 


125 


2.77 


1.09 


177 


25 


150 


2.82 


1.14 


228 


35 


200 


2.90 


1.22 


304 


48 


250 


3.00 


1.32 


406 


72.5 


250 


3.00 


1.32 


406 


72.5 


350 


3.18 


1.50 


584 


121 


350 


3.18 


1.50 


584 


121 


550 n 


3.53 


1.85 


939 


145 


350 


3.18 


1.50 


584 


145 


550 


3.53 


1.85 


939 


145 


650 


3.71 


2.03 


1117 


169 


550 


3.53 


1.85 


939 


169 


650 


3.71 


2.03 


1117 


169 


750 


3.91 


2.24 


1320 


242 


550 


3.53 


1.85 


939 


242 


650 


3.71 


2.03 


1117 


242 


750 


3.91 


2.24 


1320 


242 


900 


4.19 


2.51 


1600 


242 


1050 


4.52 


2.84 


1930 



■M 



37 
Copyright © 2001 IEEE. All rights reserved. 



T-124-lB(m) 



PART 1. ELECTRIC SUPPLY STATIONS 



T-124-lB(m) 



m 



Table 124-1 (Continued) 2 

PART B — Extra-High Voltages (based on switching-surge factors) 



Maximum 

design voltage 

between 

phases (1) 


Switching- 
surge factor 
per unit 

(A) 4 


Switching 

surge line to 

ground 

(B) 4 


Vertical 

clearance of 

unguarded 

parts (2) x 


Horizontal 

clearance of 

unguarded 

parts (3) 1 


Clearance 

guard to live 

parts 

(4) 1 






kV 


m 


m 


m 


362 000 


2.2 or below 


650 


4.7 


3.0 


2.13 




2.3 


680 


4.9 


3.2 


2.30 




2.4 


709 


5.0 


3.4 


2.45 




2.5 


739 


5.2 


3.6 


2.60 




2.6 


768 


5.4 


3.7 


2.80 




2.7 


798 


5.6 


3.9 


3.0 




2.8 


828 


5.8 


4.1 


3.2 




2.9 


857 


6.0 


4.3 


3.4 




3.0 


887 


6.1 


4.5 


3.6 


550 000 


1 .8 or below 


808 


5.7 


4.1 


3.2 




1.9 


853 


5.9 


4.3 


3.4 




2.0 


898 


6.2 


4.6 


3.6 




2.1 


943 


6.6 


4.9 


4.0 




2.2 


988 


6.9 


5.2 


4.3 




2.3 


1033 


7.2 


5.5 


4.6 




2.4 


1078 


7.5 


5.8 


4.9 




2.5 


1123 


7.9 


6.2 


5.3 




2.6 


1167 


8.2 


6.6 


5.6 




2.7 


1212 


8.6 


7.0 


6.0 


800 000 


1.5 


980 


6.8 


5.1 


4.2 




1.6 


1045 


7.3 


5.6 


4.7 




1.7 


1110 


7.8 


6.1 


5.2 




1.8 


1176 


8.3 


6.6 


5.7 




1.9 


1241 


8.8 


7.2 


6.2 




2.0 


1306 


9.4 


7.7 


6.8 




2.1 


1372 


10.0 


8.3 


7.4 




2.2 


1437 


10.6 


8.9 


8.0 




2.3 


1502 


11.2 


9.5 


8.6 




2.4 


1567 


11.8 


10.0 


9.2 



38 
Copyright © 2001 IEEE. All rights reserved. 



T-124-lC(m) 



PART 1 . ELECTRIC SUPPLY STATIONS 



T-124-lD(m) 



m 



Table 124-1 (Continued) 2 

PART C — Extra-High Voltages (based on BIL factors) 



Maximum design 

voltage between 

phases 

(1) 


Basic impulse 
insulation level 
(BIL) 

(C) 4 


Vertical 

clearance of 

unguarded parts 

(2) 1 


Horizontal 

clearance of 

unguarded parts 

(3) 1 


Clearance 
guard to 
live parts 

(4) 1 




kV 


m 


m 


m 


362 000 


1050 


4.7 


3.0 


2.13 


362 000 


1300 


5.2 


3.6 


2.60 


550 000 


1550 


5.7 


4.1 


3.2 


550 000 


1800 


6.2 


4.6 


3.6 


800 000 


2050 


6.8 


5.2 


4.2 



Table 124-1 (Continued) 
PART D — High Voltage Direct Current (Based on Transient Overvoltage) 



m 



I 



Maximum 

design voltage 

conductor to 

ground 


Transient 

overvoltage 

per unit 

(A) 4 


Transient 

overvoltage 

line to grnd 

(B) 4 


Vertical 

clearance of 

unguarded 

parts 


Horizontal 

clearance of 

unguarded 

parts 


Clearance 

guard to live 

parts 1 


kV 




kV 


m 


m 


m 


250 


1 .5 or below 


375 


3.81 


2.13 


1.22 




1.6 


400 


3.89 


2.22 


1.30 




1.7 


425 


3.97 


2.30 


1.38 




1.8 


450 


4.05 


2.38 


1.46 


400 


1 .5 or below 


600 


4.54 


2.87 


1.95 




1.6 


640 


4.67 


3.00 


2.08 




1.7 


680 


4.88 


3.21 


2.29 




1.8 


720 


5.12 


3.45 


2.53 


500 


1 .5 or below 


750 


5.29 


3.62 


2.70 




1.6 


800 


5.60 


3.92 


3.01 




1.7 


850 


5.96 


4.29 


3.37 




1.8 


900 


6.35 


4.67 


3.76 


600 


1 .5 or below 


900 


6.35 


4.67 


3.76 




1.6 


960 


6.73 


5.06 


4.14 




1.7 


1020 


7.13 


5.45 


4.54 




1.8 


1080 


7.57 


5.89 


4.97 



39 
Copyright © 2001 IEEE. All rights reserved. 



T-124-lD(m) 



PART 1 . ELECTRIC SUPPLY STATIONS 



T-124-lD(m) 



m 



Table 124-1 (Continued) 
PART D — High Voltage Direct Current (Based on Transient Overvoltage) 



Maximum 

design voltage 

conductor to 

ground 


Transient 

overvoltage 

per unit 

(A) 4 


Transient 
overvoltage 
line to grnd 

(B) 4 


Vertical 

clearance of 

unguarded 

parts 


Horizontal 

clearance of 

unguarded 

parts 


Clearance 

guard to live 

parts 1 


kV 




kV 


m 


m 


m 


750 


1 .5 or below 


1125 


7.90 


6.23 


5.31 




1.6 


1200 


8.44 


6.76 


5.85 




1.7 


1275 


9.06 


7.38 


6.47 




1.8 


1350 


9.72 


8.04 


7.13 



1 Interpolate for intermediate values. The clearances in column 4 of this table are solely for guidance in 
installing guards without definite engineering design and are not to be considered as a requirement for such 
engineering design. For example, the clearances in the tables above are not intended to refer to the clear- 
ances between live parts and the walls of the cells, compartments, or similar enclosing structures. They do 
not apply to the clearances between bus bars and supporting structures nor to clearances between the blade 
of a disconnecting switch and its base. However, where surge-protective devices are applied to protect the 
live parts, the vertical clearances, column 2 of Table 124-1 Part A may be reduced provided the clearance 
is not less than 2.6 m plus the electrical clearance between energized parts and ground as limited by the 
surge-protective devices. 

2 Clearances shall satisfy either switching-surge or BIL duty requirements, whichever are greater. 

3 Switching-Surge Factor— an expression of the maximum switching-surge crest voltage in terms of the 
maximum operating line-to-neutral crest voltage of the power system. 

4 The values of columns A, B, and C are power system design factors that shall correlate with selected 
clearances. Adequate data to support these design factors should be available. 

The selection of station BIL shall be coordinated with surge-protective devices when BIL is used to 
determine clearance. BIL— Basic Impulse Insulation Level— For definition and application, see IEEE 
Std 1313-1993. 



40 
Copyright © 2001 IEEE. All rights reserved. 



T-124-lA(ft) 



PART 1. ELECTRIC SUPPLY STATIONS 



T-124-lA(ft) 



ft 



Table 124-1 

Clearances From Live Parts 

Part A— Low, Medium, and High Voltages (based on BIL factors) 



Maximum 
Design Voltage 
between Phases 

(1) 


Basic Impulse 

Insulation Level s 

(BIL) 


Vertical 

clearance of 

unguarded parts 

(2) 1 


Horizontal 

clearance of 

unguarded parts 

(3) 1 


Clearance 

guard to live 

parts 

(4) 1 


kV 


kV 


ft 


in 


ft 


in 


ft 


in 


0.151-0.6 


— 


8 


8 


3 


4 





2 


2.4 


— 


8 


9 


3 


4 





3 


7.2 


95 


8 


10 


3 


4 





4 


15 


95 


8 


10 


3 


4 





4 


15 


110 


9 





3 


6 





6 


25 


125 


9 


1 


3 


7 





7 


25 


150 


9 


3 


3 


9 





9 


35 


200 


9 


6 


4 










48 


250 


9 


10 


4 


4 




4 


72.5 


250 


9 


10 


4 


4 




4 


72.5 


350 


10 


5 


4 


11 




11 


121 


350 


10 


5 


4 


11 




11 


121 


550 


11 


7 


6 


1 


3 


1 


145 


350 


10 


5 


4 


11 


1 


11 


145 


550 


11 


7 


6 


1 


3 


1 


145 


650 


12 


2 


6 


8 


3 


8 


169 


550 


11 


7 


6 


1 


3 


1 


169 


650 


12 


2 


6 


8 


3 


8 


169 


750 


12 


10 


7 


4 


4 


4 


242 


550 


11 


7 


6 


1 


3 


1 


242 


650 


12 


2 


6 


8 


3 


8 


242 


750 


12 


10 


7 


4 


4 


4 


242 


900 


13 


9 


8 


3 


5 


3 


242 


1050 


14 


10 


9 


4 


6 


4 



I 



41 
Copyright © 2001 IEEE. All rights reserved. 



T-124-lB(ft) 



PART 1. ELECTRIC SUPPLY STATIONS 



T-124-lB(ft) 



ft 



Table 124-1 (Continued) 
PART B — Extra-High Voltages (based on switching-surge factors) 



Maximum 

design voltage 

between 

phases 

(1) 


Switching 

surge factor 3 

per unit 

(A) 4 


Switching 

surge line to 

ground 

(B) 4 


Vertical 

clearance of 

unguarded 

parts 

(2) 1 


Horizontal 

clearance of 

unguarded 

parts 

(3) 1 


Clearance 

guard to live 

parts 

(4) 1 


kv 


ft 


in 


ft 


in 


ft 


in 


362 000 


2.2 or below 


650 


15 


6 


10 





7 







2.3 


680 


16 





10 


6 


7 


6 




2.4 


709 


16 


6 


11 





8 







2.5 


739 


17 


2 


11 


8 


8 


8 




2.6 


768 


17 


9 


12 


3 


9 


3 




2.7 


798 


18 


4 


12 


10 


9 


10 




2.8 


828 


18 


11 


13 


5 


10 


5 




2.9 


857 


19 


7 


14 


1 


11 


1 




3.0 


887 


20 


2 


14 


8 


11 


8 


550 000 


1 .8 or below 


808 


18 


10 


13 


4 


10 


4 




1.9 


853 


19 


6 


14 





11 







2.0 


898 


20 


6 


15 





12 







2.1 


943 


21 


6 


16 





13 







2.2 


988 


22 


6 


17 





14 







2.3 


1033 


23 


7 


18 


1 


15 


1 




2.4 


1078 


24 


8 


19 


2 


16 


2 




2.5 


1123 


25 


10 


20 


4 


17 


4 




2.6 


1167 


27 





21 


6 


18 


6 




2.7 


1212 


28 


4 


22 


10 


19 


10 


800 000 


1.5 


980 


22 


4 


16 


10 


13 


10 




1.6 


1045 


23 


11 


18 


5 


15 


5 




1.7 


1110 


25 


6 


20 





17 


1 




1.8 


1176 


27 


3 


21 


9 


18 


9 




1.9 


1241 


29 





23 


6 


2 


6 




2.0 


1306 


30 


10 


25 


4 


22 


4 




2.1 


1372 


32 


9 


27 


3 


24 


3 




2.2 


1437 


34 


8 


29 


3 


26 


2 




2.3 


1502 


36 


9 


31 


3 


28 


3 




2.4 


1567 


38 


9 


33 


3 


30 


3 



42 
Copyright © 2001 IEEE. All rights reserved. 



T-124-lC(ft) 



PART 1 . ELECTRIC SUPPLY STATIONS 



T-124-lD(ft) 



Table 124-1 (Continued) 
PART C — Extra-High Voltages (based on BIL factors) 2 



ft 



Maximum 

design voltages 

between 

phases 

(1) 


Basic impulse 
insulation 

level 5 (BIL) 

(C) 4 


Vertical 

clearance of 

unguarded parts 

(2) 1 


Horizontal 

clearance of 

unguarded parts 

(3) 1 


Clearance 
guard to 
live parts 

(4) 1 


kV 


ft 


in 


ft 


in 


ft 


in 


362 000 


1050 


15 


6 


10 





7 





362 000 


1300 


17 


2 


11 


8 


8 


8 


550 000 


1550 


18 


10 


13 


4 


10 


4 


550 000 


1800 


20 


6 


15 





12 





800 000 


2050 


22 


5 


16 


11 


13 


11 



ft 



Table 124-1 (Continued) 
PART D — High Voltage Direct Current (Based on Transient Overvoltage) 



I 



Maximum 

design voltage 

conductor to 

ground 


Transient 

overvoltage 

per unit 

(A) 4 


Transient 
overvoltage 
line to grnd 

(B) 4 


Vertical 

clearance of 

unguarded 

parts 


Horizontal 

clearance of 

unguarded 

parts 


Clearance 

guard to live 

parts 1 


kV 




kV 


ft 


in 


ft 


in 


ft 


in 


250 


1 .5 or below 


375 


12 


6 


7 





4 







1.6 


400 


12 


9 


7 


3 


4 


3 




1.7 


425 


13 





7 


7 


4 


6 




1.8 


450 


13 


3 


7 


10 


4 


9 


400 


1 .5 or below 


600 


14 


11 


9 


5 


6 


5 




1.6 


640 


15 


4 


9 


10 


6 


10 




1.7 


680 


16 





10 


6 


7 


6 




1.8 


720 


16 


10 


11 


4 


8 


4 


500 


1 .5 or below 


750 


17 


4 


11 


11 


8 


10 




1.6 


800 


18 


4 


12 


10 


9 


11 




1.7 


850 


19 


7 


14 


1 


11 


1 




1.8 


900 


20 


10 


15 


4 


12 


4 


600 


1 .5 or below 


900 


20 


10 


15 


4 


12 


4 




1.6 


960 


22 


1 


16 


7 


13 


7 




1.7 


1020 


23 


5 


17 


11 


14 


11 




1.8 


1080 


24 


10 


19 


4 


16 


4 


750 


1 .5 or below 


1125 


25 


11 


20 


5 


17 


5 




1.6 


1200 


27 


8 


22 


2 


19 


2 



43 
Copyright © 2001 IEEE. All rights reserved. 



T-124-lD(ft) 



PART 1. ELECTRIC SUPPLY STATIONS 



F-124-2 



ft 



Table 124-1 (Continued) 
PART D — High Voltage Direct Current (Based on Transient Overvoltage) 



Maximum 

design voltage 

conductor to 

ground 


Transient 

overvoltage 

per unit 

(A) 4 


Transient 
overvoltage 
line to grnd 

(B) 4 


Vertical 

clearance of 

unguarded 

parts 


Horizontal 

clearance of 

unguarded 

parts 


Clearance 

guard to live 

parts 


kV 




kV 


ft 


in 


ft 


in 


ft 


in 




1.7 


1275 


29 


9 


24 


3 


21 


3 




1.8 


1350 


31 


11 


26 


5 


23 


5 



1 Interpolate for intermediate values. The clearances in column 4 of this table are solely for guidance in 
installing guards without definite engineering design and are not to be considered as a requirement for such 
engineering design. For example, the clearances in the tables above are not intended to refer to the clear- 
ances between live parts and the walls of the cells, compartments, or similar enclosing structures. They do 
not apply to the clearances between bus bars and supporting structures nor to clearances between the blade 
of a disconnecting switch and its base. However, where surge-protective devices are applied to protect the 
live parts , the vertical clearances , column 2 of Table 1 24- 1 Part A may be reduced provided the clearance 
is not less than 8.5 ft plus the electrical clearance between energized parts and ground as limited by the 
surge-protective devices. 

2 Clearances shall satisfy either switching-surge or BIL duty requirements, whichever are greater. 

3 Switching-Surge Factor— an expression of the maximum switching-surge crest voltage in terms of the 
maximum operating line-to-neutral crest voltage of the power system. 

4 The values of columns A, B, and C are power system design factors that shall correlate with selected 
clearances. Adequate data to support these design factors should be available. 

The selection of station BIL shall be coordinated with surge-protective devices when BIL is used to 
determine clearance. BIL— Basic Impulse Insulation Level— For definition and application, see IEEE 
Std 1313-1993. 



LIVE CONDUCTOR 



RAILING 

REQUIRED 

HERE 



2.60 m (8 ft, 6 in) 




1 LESS THAN 

1 2.60 m (8 ft, 6 in) 




1.20 mi (4 ft) 



Fig 124-2 
Railing Used as Guards 



44 
Copyright © 2001 IEEE. All rights reserved. 



125 



PART 1. ELECTRIC SUPPLY STATIONS 



125B 



125. Working Space About Electric Equipment 

A. Working Space (600 V or Less) 

Access and working space shall be provided and maintained about electric equipment to permit ready 
and safe operation and maintenance of such equipment. 

1 . Clear Spaces 

Working space required by this section shall not be used for storage. When normally enclosed 
energized parts are exposed for inspection or servicing, the working space, if in a passageway or 
general open space, shall be guarded. 

2. Access and Entrance to Working Space 

At least one entrance shall be provided to give access to the working space about electric 
equipment. 

3. Working Space 

The working space in the direction of access to energized parts operating at 600 V or less that 
require examination, adjustment, servicing, or maintenance while energized shall be not less than 
indicated in Table 125-1 . In addition to the dimensions shown in Table 125-1 , the working space 
shall be not less than 750 mm (30 in) wide in front of the electric equipment. Distances shall be 
measured from the energized parts if such are exposed or from the enclosure front or opening if 
such are enclosed. Concrete, brick, or tile walls shall be considered grounded. 

4. Headroom Working Space 

The headroom of working spaces about switchboards or control centers shall be not less than 
2.13 m (7 ft). 

5. Front Working Space 

In all cases where there are energized parts normally exposed on the front of switchboards or mo- 
tor control centers, the working space in front of such equipment shall not be less than 900 mm 
(3 ft). 

Table 125-1 
Working Space 






Voltage to 
ground 


Condition 


Clear Distance 


(mm) 
1 


(ft) 
1 


(mm) 
2 


(ft) 
2 


(mm) 
3 


(it) 

:: : : .;3. ■:.': 


0-150 




900 


3 


900 


900 


3 

r7 ", 4 '■.'.'■. 


151-600 




900 


3 


1070 


3-1/2 


1200 



Where the Conditions are as follows: 

1 . Exposed energized parts on one side and no energized or grounded parts on the other side of the working 
space, or exposed energized parts on both sides effectively guarded by suitable wood or other insulating 
materials. Insulated wire or insulated bus bars operating at not over 300 V shall not be considered ener- 
gized parts. 

2. Exposed energized parts on one side and grounded parts on the other side. 

3. Exposed energized parts on both sides of the work space (not guarded as provided in Condition 1) with 
the operator between. 

EXCEPTION: Working space shall not be required in back of assemblies, such as dead-front switchboards 
or motor control centers where there are no renewable or adjustable parts such as fuses or switches on the 
back and where all connections are accessible from locations other than the back. 

B. Working Space Over 600 V 

Working space shall be in accordance with Table 124-1 clearances for guarding. 



45 
Copyright © 2001 IEEE. All rights reserved. 



1 26 PART 1 . ELECTRIC SUPPLY STATIONS 1 27B3c 



126. Equipment for Work on Energized Parts 

When it is necessary for personnel to move themselves, material, or tools within the guard zone of 
unguarded energized parts, protective equipment shall be provided. 

This protective equipment shall be periodically inspected, tested, and kept in a safe condition. Pro- 
tective equipment shall be rated for not less than the voltage involved. Refer to Section 3 for a list of 
specifications for equipment. 

127. Classified Locations 

Electrical installations in classified areas shall meet the requirements of the National Electrical Code 
(NEC) (NFPA 70-1999), Articles 500 through 517. Areas classified in accordance with NEC Article 
500 shall comply with the requirements of that Article and A. through L. below. Areas classified with 
the optional Zone method in accordance with NEC Article 505 shall comply with the requirements of 
that article. 

A. Coal-Handling Areas 

1 . Un ventilated spaces inside or above coal-storage silos or bunkers, or other enclosed coal-storage 
and coal-handling spaces where methane may accumulate in explosive or ignitable mixtures as de- 
fined in Article 500-5 of the NEC, are Class I, Division 1 , Group D locations. Electric equipment 
in other locations in which flammable gases or vapors may exist shall be in accordance with the 
NEC, Article 500-5, or the locations shall be adequately ventilated 

2. Adequate ventilation exists when the method of ventilation will limit the likelihood of 
accumulation of significant quantities of vapor-air concentrations from exceeding 25% of the 
lower flammable limit. 

3. Tunnels beneath stockpiles or surge piles; spaces inside, above, or below coal-storage silos or bun- 
kers; or other enclosed coal-storage or coal-handling spaces or areas shall be Class n, Group F, 
Division 1 or Division 2 locations as determined by the NEC. 

4. Enclosed sections where only wet coal is handled, or enclosed sections so cut off as to be free from 
dangerous amounts of coal dust, are not classified. Coal shall be considered to be wet if enough 
water sprays are installed and maintained to limit the atmospheric concentration of total entrapped 
volatiles to 8% or less. (See ASTM D 3175 for coal and coke dusts). 

5. Locations having completely dust-tight pulverized fuel systems designed and installed in compli- 
ance with NFPA 8503-1997 shall not be considered classified. 

6. Portable lamps for use in fuel bunkers or bins shall be suitable for Class II, Division 1 locations. 

7. Sparking electric tools shall not be used where combustible dust or dust clouds are present. 

8. An equipment grounding conductor shall be carried with the power conductors and serve to 
ground the frames of all equipment supplied from that circuit. The origin of the grounding con- 
ductor shall be: 

a. Ungrounded delta or wye-transformer frame ground. 

b. Grounded delta or wye-transformer grounded secondary connection. 

c. Resistance grounded wye— the grounded side of the grounding resistor. 

9. Ungrounded systems should be equipped with a ground-fault indicating device to give both a vi- 
sual and audible alarm upon the occurrence of a ground fault in the system. 

B . Flammable and Combustible Liquids 

1 . Flammable liquid shall mean a liquid having a flash point below 38 °C (100 °F) and having a va- 
por pressure not exceeding 275 kPa (40 lb/in 2 ) (absolute) at 38 °C (100 °F) and shall be known as 
a Class I liquid. 

2. Combustible liquid shall mean a liquid having a flash point greater than or equal to 38 °C (100 °F) 
and having a vapor pressure not exceeding 275 kPa (40 lb/in 2 ) (absolute) at 38 °C (100 °F). 

3. Class I liquids are subdivided as follows: 

a. Class IA includes those having flash points below 23 °C (73 °F) and having a boiling point 
below 38 °C (100 °F). 

b. Class IB includes those having flash points below 23 °C (73 C F). 

c. Class IC includes those having flash points at or above 23 °C (73 °F) and below 38 °C 
(100 °F). 

46 
Copyright © 2001 IEEE. All rights reserved. 



1 27B4 PART 1 . ELECTRIC SUPPLY STATIONS 1 27G3 

4. Combustible liquids are subdivided as follows: 

a. Class II includes those having flash points equal to or greater than 38 °C (100 °F) but less than 
60°C(140°F). 

b. Class IIIA includes those having flash points equal to or greater than 60 °C (140 °F) but less 
than 93 °C (200 °F). 

c. Class IIIB includes those having flash points greater than or equal to 93 °C (200 °F). 

C. Flammable Liquid Storage Area 

Electric wiring and equipment located in flammable liquid storage areas shall be installed in accor- 
| dance with applicable sections of NFPA 30-2000 and the NEC . 

D. Loading and Unloading Facilities for Flammable and Combustible Liquids 

Electric equipment located in the area shall be installed in accordance with applicable sections of 
| NFPA 30-2000 and the NEC . 

E. Gasoline-Dispensing Stations 

Electric equipment installed in areas used for dispensing flammable liquids shall be installed in accor- 
| dance with applicable sections of NFPA 30A-2000 and the NEC . 

F. Boilers 

When storing, handling, or burning fuel oils that have flash points below 38 °C (100 °F) the installa- 
| tion shall conform to NFPA 30-2000 and the NEC. 

NOTE: Attention must be given to electrical installations in areas where flammable vapors or gases may be 
present in the atmosphere. Typical locations are burner areas, fuel-handling equipment areas, fuel-storage areas, 
pits, sumps, and low spots where fuel leakage or vapors may accumulate. The NEC, Article 500 provides for 
classifying such areas and defines requirements for electrical installations in the areas so classified. The burner 
front piping and equipment shall be designed and constructed to eliminate hazardous concentrations of 
flammable gases that exist continuously, intermittently, or periodically under normal operating conditions. 
Providing the burners are thoroughly purged before removal for cleaning, burner front maintenance operations 
will not cause hazardous concentrations of flammable vapors to exist frequently. With such provisions , the burner 
front is not normally classified more restrictively than Class I, Division 2. 

G. Gaseous Hydrogen Systems for Supply Equipment 

1 . Outdoor storage areas shall not be located beneath electric power lines. 

2. Safety considerations at specific storage areas. 

Electric equipment shall be suitable for Class I, Division 2 locations: 

a. Within 4.6 m (15 ft) of outdoor storage spaces 

b. Within adequately ventilated separate buildings or special rooms for storing hydrogen 

c. Within 7.6 m (25 ft) of a hydrogen storage space in an adequately ventilated building used for 
other purposes 

3 . Space around elements of the generator hydrogen seal oil system shall not be considered classified 
for electrical installation except where external venting is not provided in the bearing drain 
system. 

47 
Copyright © 2001 IEEE. All rights reserved. 



I 



127G4 PART 1 . ELECTRIC SUPPLY STATIONS 129 



4. Spaces around the hydrogen piping system beyond the point where the hydrogen storage system 
connects to distribution piping shall not be considered classified for electrical installations, out- 
side the boundaries established in 127G2a and 127G2c. 

H. Liquid Hydrogen Systems 

1 . Electric wiring and equipment located within 900 mm (3 ft) of a point where connections are reg- 
ularly made and disconnected shall be in accordance with the NEC, Article 501 , Class I, Group 
B, Division 1 locations. 

2. Except as provided in Paragraph 1 , electric wiring and equipment located within 7.6 m (25 ft) of 
a point where connections are regularly made and disconnected or within 7.6 m (25 ft) of a liquid 
hydrogen storage container, shall be in accordance with the NEC, Article 501, Class I, Group B, 
Division 2 locations. When equipment approved for Class I, Group B atmospheres is not com- 
mercially available, the equipment may be (1) purged or ventilated in accordance with NFPA 
496-1998, (2) intrinsically safe, or (3) approved for Class I, Group C atmospheres. This require- 
ment does not apply to electric equipment that is installed on mobile supply trucks or tank cars 
from which the storage container is filled. 

I. Sulfur 

1 . Electric wiring and equipment located in areas where sulfur dust is in suspension in explosive or 
ignitable mixtures during normal operations shall be suitable for Class II, Division 1 , Group G. 

I. Oxygen 

1 . Bulk oxygen installations are not defined as classified locations. 

K. Liquefied Petroleum Gas (LPG) 

Electric equipment and wiring installed in areas used for handling , storage , or utilization of LPG shall 
be installed in accordance with applicable sections of NFPA 58-1998, NFPA 59-1998, and the NEC. 

L. Natural Gas (Methane) 

Electric equipment and wiring installed in areas used for handling, storage, or utilization of natural 
gas shall be installed in accordance with applicable sections of NFPA 59A-1990 and the NEC. 

NOTE: NFPA 497M-1997 [B41] and API RP500, 7 January 1998 [B9], provide additional guidelines for clas- 
sifying these areas. 

128. Identification 

Electric equipment and devices shall be identified for safe use and operation. The identification shall 
be as nearly uniform as practical throughout any one station. Identification marks shall not be placed 
on removable covers or doors that could be interchanged. 

129. Mobile Hydrogen Equipment 

Mobile hydrogen supply units being used to replenish a hydrogen system shall be bonded both to the 
grounding system and to the grounded parts of the hydrogen system. 



48 
Copyright © 2001 IEEE. All rights reserved. 



130 PART 1 . ELECTRIC SUPPLY STATIONS 133 

Section 13. 
Rotating Equipment 

Rotating equipment includes generators, motors, motor generators, and rotary converters. 

130. Speed Control and Stopping Devices 

A. Automatic Overspeed Trip Device for Prime Movers 

When harmful overspeed can occur, prime movers driving generating equipment shall be provided 
with automatic overspeed trip devices in addition to their governors. 

B. Manual Stopping Devices 

An operator-initiated stopping device shall be provided for any machine that drives an electric power 
generator or rotary uninterruptible power supply (motor-generator). The operator-initiated stopping 
device shall be accessible to the operator during normal operation. Manual controls to be used in 
emergency for machinery and electric equipment shall be located so as to provide protection to the 
operator in the event of such emergency. 

C. Speed Limit for Motors 

Machines of the following types shall be provided with speed-limiting devices unless their inherent 
characteristics or the load and the mechanical connection thereto are such as to safely limit the speed. 

1. Separately excited dc motors 

2. Series motors 

D. Number 130D not used in this edition. 

E. Adjustable-Speed Motors 

Adjustable-speed motors, controlled by means of field regulation, shall, in addition to the provisions 
of Rule 130C, be so equipped and connected that the field cannot be weakened sufficiently to permit 
dangerous speed. 

F. Protection of Control Circuits 

Where speed-limiting or stopping devices and systems are electrically operated, the control circuits 
by which such devices are actuated shall be protected from mechanical damage. Such devices and sys- 
tems should be of the automatic tripping type. 

131. Motor Control 



All motors arranged such that an unexpected starting of the motor might create an exposure of 
personnel to injury shall have the motor control circuit designed to block unintended re-energization of 
the motor after a power supply interruption of a duration sufficient for moving equipment to become 
stationary. The motor control shall be such that an operator must take some action to restart the motor, 
or automatic restarting shall be preceded by warning signals and a time delay sufficient for personnel 
action to limit the likelihood of injury. This requirement does not apply to those motors with an 
emergency use and where the opening of the circuit may cause less safe conditions. 

132. Number 132 not used in this edition. 

133. Short-Circuit Protection 

Means shall be provided to automatically disconnect an electric motor from the supply source in the 
event of high-magnitude short-circuit currents within the motor. 

49 
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140 PARTI. ELECTRIC SUPPLY STATIONS 147 

Section 14. 
Storage Batteries 



140. General 

The provisions of this section are intended to apply to all stationary installations of storage batteries. 
For operating precautions, see Part 4 of this code. 

Space shall be provided around batteries for safe inspection, maintenance, testing, and cell re- 
placement and space left above the cells to allow for operation of lifting equipment when required, 
addition of water, and taking measurements. 

141. Location 

Storage batteries shall be located within a protective enclosure or area accessible only to qualified 
persons. A protective enclosure can be a battery room, control building, or a case, cage, or fence that 
will protect the contained equipment and limit the likelihood of inadvertent contact with energized 
parts. 

142. Ventilation 

The battery area shall be ventilated, either by a natural or powered ventilation system to limit 
hydrogen accumulation to less than an explosive mixture. Failure of a continuously operated or 
automatically controlled powered ventilation system required by design to limit hydrogen 
accumulation to less than an explosive mixture shall be annunciated. 

143. Racks 

Racks refer to frames designed to support cells or trays. Racks shall be firmly anchored, preferably 
to the floor. Anchoring to both walls and floors is not recommended. Racks made of metal shall be 
grounded. 

144. Floors in Battery Areas 

Floors of battery areas should be of an acid-resistive material, painted with acid-resistive paint, or 
otherwise protected. Provision should be made to contain spilled electrolyte. 

145. Illumination for Battery Areas 

Lighting fixtures shall be protected from physical damage by guards or isolation. Receptacles and 
lighting switches should be located outside of battery areas. 

146. Service Facilities 

A. Proper eye protection and clothing shall be provided in the battery area during battery maintenance 
and installation and shall consist of the following: 

1. Goggles or face shield 

2. Acid-resistant gloves 

3. Protective aprons and overshoes 

4. Portable or stationary water facilities or neutralizing agent for rinsing eyes and skin 

B . Safety signs inside and outside of a battery room or in the vicinity of a battery area, prohibiting smok- 
ing, sparks, or flame shall be provided. 

NOTE: ANSI Z535.1-1998, ANSI Z535.2-1998, ANSI Z535.3-1998, ANSI Z535.4-1998, and ANSI Z535.5- 
1998 contain information regarding safety signs. 

147. Number 147 not used in this edition. 

50 
Copyright © 2001 IEEE. All rights reserved. 



150 PARTI. ELECTRIC SUPPLY STATIONS 153 



Section 15. 
Transformers and Regulators 



150. Current-Transformer Secondary Circuits Protection When Exceeding 600 V 

Secondary circuits, when in the vicinity of primary circuits exceeding 600 V should, except for short 
lead lengths at the terminals of the transformer, have the secondary wiring adequately protected by 
means of conduit, covering, or some other protection. Any metallic covering used shall be effectively 
grounded, giving appropriate consideration to circulating currents. Current transformers shall have 
provision for shorting the secondary winding. 

151. Grounding Secondary Circuits of Instrument Transformers 

The secondary circuits of instrument transformers shall be effectively grounded where functional re- 
quirements permit. 

152. Location and Arrangement of Power Transformers and Regulators 

A. Outdoor Installations 

1. Power transformers and regulators shall be so installed that all energized parts are enclosed or 
guarded so as to limit the likelihood of inadvertent contact, or the energized parts shall be physi- 
cally isolated in accordance with Rule 124. The case shall be effectively grounded or guarded. 

2. The installation of liquid-filled transformers shall utilize one or more of the following methods 
to minimize fire hazards. The method to be applied shall be according to the degree of the fire 
hazard. Recognized methods are the use of less flammable liquids, space separation, fire-resistant 
barriers, automatic extinguishing systems, absorption beds, and enclosures. 

The amount and characteristics of liquid contained should be considered in the selection of 
space separation, fire-resistant barriers, automatic extinguishing systems, absorption beds, and 
enclosures that confine the liquid of a ruptured transformer tank, all of which are recognized as 
safeguards. 

B. Indoor Installations 

1. Transformers and regulators 75 kVA and above containing an appreciable amount of flammable 
liquid and located indoors shall be installed in ventilated rooms or vaults separated from the bal- 
ance of the building by fire walls. Doorways to the interior of the building shall be equipped with 
fire doors and shall have means of containing the liquid. 

2. Transformers or regulators of the dry type or containing a nonflammable liquid or gas may be in- 
stalled in a building without a fireproof enclosure. When installed in a building used for other than 
station purposes, the case or the enclosure shall be so designed that all energized parts are en- 
closed in the case that is grounded in accordance with Rule 123. As an alternate, the entire unit 
may be enclosed so as to limit the likelihood of inadvertent contact by persons with any part of 
the case or wiring. When installed, the pressure-relief vent of a unit containing a nonbiodegrad- 
able liquid shall be furnished with a means for absorbing toxic gases. 

3. Transformers containing less flammable liquid may be installed in a supply station building in 
such a way as to minimize fire hazards. The amount of liquid contained, the type of electrical pro- 
tection, and tank venting shall be considered in the selection of space separation from combusti- 
ble materials or structures, liquid confinement, fire-resistant barriers or enclosures, or 
extinguishing systems. 

153. Short-Circuit Protection of Power Transformers 

Power transformers shall be provided with means to disconnect automatically the source of supply of 
current for a high magnitude short circuit (fault) within the transformer. 

The devices for automatically disconnecting the source of supply may be a circuit breaker, circuit 
switcher, fuse, thyristor blocking, or other reasonable methods either locally or remotely connected 
to the transformer. This includes disconnecting the generator electric field source together with the 

51 
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153 PARTI. ELECTRIC SUPPLY STATIONS 153 



source of mechanical energy upon detection of a fault in either the generator step-up or station aux- 
iliary transformer. Removing a single phase rather than all three phases to extinguish short-circuit 
current is acceptable. 

EXCEPTION: Transformers other than power transformers are exempt from this rule. This includes instrument 
transformers, neutral grounding transformers, regulating transformers, and other transformers specifically for 
control, protection, or metering. 



52 
Copyright © 2001 IEEE. All rights reserved. 



160 PARTI. ELECTRIC SUPPLY STATIONS 164B 



Section 16. 
Conductors 



160. Application 

Conductors shall be suitable for the location, use, and voltage. Conductors shall have ampacity that 
is adequate for the application. 

161. Electrical Protection 

A. Overcurrent Protection Required 

Conductors and insulation shall be protected against excessive heating by the design of the system 
and by overcurrent, alarm, indication, or trip devices. 

B. Grounded Conductors 

Conductors normally grounded for the protection of persons shall be arranged without overcurrent 
protection or other means that could interrupt their continuity to ground. 

C. Insulated Power Cables 

Insulated power cable circuits shall be provided with short-circuit protection that will isolate the short 
circuit from the supply. 

162. Mechanical Protection and Support 

A. All conductors shall be adequately supported to withstand forces caused by the maximum short- 
circuit current to which they may be subjected. Where support conductors extend outside the electric 
supply station, such conductors and their supports shall comply with the grades of construction, 
strength, and loading requirements of Part 2 of this code. 

B. Where conductors, conductor insulation, or conductor supports may be subjected to mechanical 
damage, casing, armor, or other means shall be employed to limit the likelihood of damage or 
disturbance. 

163. Isolation 

All nonshielded insulated conductors of more than 2500 V to ground and bare conductors of more 
than 150 V to ground shall be isolated by elevation or guarded in accordance with Rule 124. 

Nonshielded, insulated, and jacketed conductors may be installed in accordance with 
Rule 124C6. 

164. Conductor Terminations 

A. Insulation 

Ends and joints of insulated conductors, unless otherwise adequately guarded, shall have insulating 
covering equivalent to that of other portions of the conductor. 

B. Metal-Sheathed or Shielded Cable 

Insulation of the conductors, where leaving the metal sheath or shield, shall be protected from me- 
chanical damage, moisture, and excessive electrical stress. 



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53 
Copyright © 2001 IEEE. All rights reserved. 



170 PARTI. ELECTRIC SUPPLY STATIONS 174B 

Section 17. 
Circuit Breakers, Reclosers, Switches, and Fuses 

170. Arrangement 

Circuit breakers, reclosers, switches, and fuses shall be so installed as to be accessible only to persons 
qualified for operation and maintenance. Walls, barriers, latched doors, location, isolation, or other 
means shall be provided to protect persons from energized parts or arcing. Conspicuous markings 
(such as numbers/letters/symbols) shall be provided on each device and at any remote operating 
points so as to facilitate identification by employees authorized to operate the device. No device iden- 
tification shall be duplicated within the same supply station. When the contact parts of a switching 
device are not normally visible, the device shall be equipped with an indicator to show all normal 
operating positions. 

171. Application 

Circuit breakers, circuit switchers, reclosers, switches, and fuses should be utilized with due regard 
to their assigned ratings of voltage and continuous and momentary currents. Devices that are intended 
to interrupt fault current shall be capable of safely interrupting the maximum short-circuit current 
they are intended to interrupt, and for the circumstances under which they are designed to operate. 
The interrupting capacity should be reviewed prior to each significant system change. 

172. Circuit Breakers, Reclosers, and Switches Containing Oil 

Circuit-interrupting devices containing flammable liquids shall be adequately segregated from other 
equipment and buildings to limit damage in the event of an explosion or fire. Segregation may be pro- 
vided by spacing, by fire-resistant barrier walls, or by metal cubicles. Gas-relief vents should be 
equipped with oil-separating devices or piped to a safe location. Means shall be provided to control 
oil that could be discharged from vents or by tank rupture. This may be accomplished by absorption 
beds, pits, drains, or by any combination thereof. Buildings or rooms housing this equipment shall be 
of fire-resistant construction. 

173. Switches and Disconnecting Devices 

A. Capacity 

Switches shall be of suitable voltage and ampere rating for the circuit in which they are installed. 
Switches used to break load current shall be marked with the current that they are rated to interrupt. 

B. Provisions for Disconnecting 

Switches and disconnectors shall be so arranged that they can be locked in the open and closed posi- 
tions, or plainly tagged where it is not practical to install locks. (See Part 4 of this code). For devices 
that are operated remotely and automatically, the control circuit shall be provided with a positive dis- 
connecting means near the apparatus to limit the likelihood of accidental operation of the mechanism. 

C. Visible Break Switch 

A visible break switch or disconnector shall be inserted in each ungrounded conductor between elec- 
tric supply equipment or lines and sources of energy of more than 600 V, if the equipment or lines 
may have to be worked on without protective grounding while the sources may be energized. 

Where metal-clad switchgear equipment is used, the withdrawn position of the circuit breaker, 
where clearly indicated, constitutes a visible break for this purpose. 

174. Disconnection of Fuses 

Fuses in circuits of more than 150 V to ground or more than 60 A shall be classified as disconnecting 
fuses or be so arranged that before handling: 

A. The fuses can be disconnected from all sources of electric energy, or 

B. The fuses can be conveniently removed by means of insulating handles. 

Fuses can be used to disconnect from the source when they are so rated. 

54 
Copyright © 2001 IEEE. All rights reserved. 



180 PARTI. ELECTRIC SUPPLY STATIONS 180B7 

Section 18. 
Switchgear and Metal-Enclosed Bus 



180. Switchgear Assemblies 

A. General Requirements for All Switchgear 

1. ; To minimize movement, all switchgear shall be secured in a manner consistent with conditions 
of service and applicable manufacturer's instructions. 

2. Cable routed to switchgear shall be supported to minimize forces applied to conductor terminals. 

3. Piping containing liquids, or corrosive or hazardous gases, shall not be routed in the vicinity of 
switchgear unless suitable barriers are installed to protect the switchgear from damage in the 
event of a pipe failure. 

4. Switchgear shall not be located where foreign flammable or corrosive gases or liquids routinely 
and normally are discharged. Companion equipment such as transformers and switchgear are not 
considered foreign. 

5. Switchgear should not be installed in a location that is still specifically under active construction, 
especially where welding and burning are required directiy overhead. Special precautions should 
be observed to minimize impingement of slag, metal filings, moisture, dust, or hot particles. 
EXCEPTION: Switchgear may be installed in a general construction area if suitable temporary protection is 
provided to minimize the risks associated with general construction activities. 

6. Precautions shall be taken to protect energized switchgear from damage when maintenance is per- 
formed in the area. 

7. Switchgear enclosure surfaces shall not be used as physical support for any item unless specifi- 
cally designed for that purpose. 

8. Enclosure interiors shall not be used as storage areas unless specifically designed for that purpose. 

9. Metal instrument cases shall be grounded and enclosed in covers that are metal and grounded, or 
are of insulating material. 

B. Metal-Enclosed Power Switchgear 

1. Switchgear shall not be located within 7.6 m (25 ft) horizontally indoors or 3.0 m (10 ft) outdoors 
of storage containers, vessels, utilization equipment, or devices containing flammable liquids or 
gases. 

EXCEPTION: If an intervening barrier, designed to mitigate the potential effects of flammable liquids or 
gases, is installed, the distances listed above do not apply. 

The restrictions are not intended to apply to the power transformer(s) supplying the switchgear. 

2. Enclosed switchgear rooms shall have at least two means of egress, one at each extreme of the 
area, not necessarily in opposite walls. Doors shall swing out and be equipped with panic bars, 
pressure plates, or other devices that are normally latched but open under simple pressure. 
EXCEPTION: One door may be used when required by physical limitations if means are provided for un- 
hampered exit during emergencies. 

3. Space shall be maintained in front of switchgear to allow breakers to be removed and turned with- 
out obstruction. 

4. Space shall be maintained in the rear of the switchgear to allow for door opening to at least 90 
degrees open, or a minimum of 900 mm (3 ft) without obstruction when removable panels are 
used. 

5. Permanently mounted devices, panelboards, etc., located on the walls shall not encroach on the 
space requirements in 180B4. 

6. Where columns extend into the room beyond the wall surface, the face of the column shall not 
encroach on the space requirements in 180B4. 

7. Low-voltage cables or conductors, except those to be connected to equipment within the 
compartment, shall not be routed through the medium- or high- voltage divisions of switchgear 
unless installed in rigid metal conduit or isolated by rigid metal barriers. 

55 
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PART 1. ELECTRIC SUPPLY STATIONS 181B2 



8. Low-voltage conductors routed from medium- or high-voltage sections of switchgear shall termi- 
nate in a low-voltage section before being routed external to the switchgear. 

9. Conductors entering switchgear shall be insulated for the higher operating voltage in that compart- 
ment or be separated from insulated conductors of other voltage ratings. 

10. Switchgear enclosures shall be suitable for the environment in which they are installed. 

1 1 . A safety sign shall be placed in each cubicle containing more than one high- voltage source. 
NOTE: ANSI Z535. 1-1998, ANSI Z535.2-1998, ANSI Z535.3-1998, ANSI Z535.4-1998, and ANSI Z535.5- 
1998 contain information regarding safety signs. 

12. The location of control devices shall be readily accessible to personnel. Instruments, relays, and 
other devices requiring reading or adjustments should be so placed that work can readily be per- 
formed from the working space. 

C. Dead-Front Power Switchboards 

Dead-front power switchboards with uninsulated rear connections shall be installed in rooms or spac- 
es that are capable of being locked, with access limited to qualified personnel. 

D. Motor Control Centers 

1 . Motor control centers shall not be connected to systems having higher short-circuit capability than 
the bus bracing can withstand. Where current-limiting fuses are employed on the source side of 
the bus, the bus bracing and breaker-interrupting rating are determined by the peak let-through 
characteristic of the current-limiting fuse. 

2. A safety sign shall be placed in each cubicle containing more than one voltage source. 

NOTE: ANSI Z535. 1-1998, ANSI Z535.2-1998, ANSI Z535.3-1998, ANSI Z535.4-1998, and ANSI Z535.5- 
1998 contain information regarding safety signs. 

E. Control Switchboards 

1. Cabinets containing solid-state logic devices, electron tubes, or relay logic devices such as boiler 
analog, burner safety, annunciators, computers, inverters, precipitator logic, soot blower control, 
load control, telemetering, totalizing microwave radio, etc., are covered under these rules. 

2. Where carpeting is installed in rooms containing control switchboards, it shall be of an antistatic 
type and shall minimize the release of noxious, corrosive, caustic, or toxic gas under any 
condition. 

3. Layout of the installation shall provide adequate clearance in front of, or rear of, panels if appli- 
cable, to allow meters to be read without use of stools or auxiliary devices. 

4. Where personnel access to control panels, such as benchboards, is required, cables shall be routed 
through openings separate from the personnel opening. Removable, sliding, or hinged panels are 
to be installed to close the personnel opening when not in use. 

181. Metal-Enclosed Bus 

A. General Requirements for All Types of Bus 

1. Busways shall be installed only in accessible areas. 

2. Busways, unless specifically approved for the purpose, shall not be installed: where subject to 
severe physical damage or corrosive vapors; in hoistways; in any classified hazardous location; 
outdoors or in damp locations. 

3. Deadends of busway shall be closed. 

4. Busways should be marked with the voltage and current rating for which they are designed, in 
such manner as to be visible after installation. 

B. Isolated-Phase Bus 

1 . The minimum clearance between an isolated-phase bus and any magnetic material shall be the dis- 
tance recommended by the manufacturer to avoid overheating of the magnetic material. 

2. Nonmagnetic conduit should be used to protect the conductors for bus-alarm devices, thermocou- 
ples, space heaters, etc., if routed within the manufacturer's recommended minimum distance to 
magnetic material and parallel to isolated-phase bus enclosures. 

56 
Copyright © 2001 IEEE. All rights reserved. 



181B3 PARTI. ELECTRIC SUPPLY STATIONS 181B5 



3. When enclosure drains are provided for isolated-phase bus, necessary piping shall be provided to 
divert water away from electrical equipment. 

4. Wall plates for isolated-phase bus shall be nonmagnetic, such as aluminum or stainless steel. 

5. Grounding conductors for isolated-phase bus accessories should not be routed through ferrous 
conduit. 



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57 
Copyright © 2001 IEEE. All rights reserved. 



190 PARTI. ELECTRIC SUPPLY STATIONS 193 



Section 19. 
Surge Arresters 



190. Genera] Requirements 

If arresters are required, they shall be located as close as practical to the equipment they protect. 
NOTE: See IEEE Std C62.1-1989 [B37] and IEEE Std C62.1 1-1999 [B38] for additional information. 

191. Indoor Locations 

Arresters, if installed inside of buildings, shall be enclosed or shall be located well away from pas- 
sageways and combustible parts. 

192. Grounding Conductors 

Grounding conductors shall be run as directly as practical between the arresters and ground and be of low 
impedance and ample current-carrying capacity and shall be grounded in accordance with the methods 
outlined in Section 9. 

193. Installation 

Arresters shall be installed in such a manner and location that neither the expulsion of gases nor the 
arrester disconnector is directed upon live parts in the vicinity. 



58 
Copyright © 2001 IEEE. All rights reserved. 



200 PART 2. SAFETY RULES FOR OVERHEAD LINES 202 

Part 2. 

Safety Rules for the Installation and 

Maintenance of Overhead Electric 

Supply and Communication Lines 

Section 20. 
Purpose, Scope, and Application of Rules 

200. Purpose 

The purpose of Part 2 of this code is the practical safeguarding of persons during the installation, op- 
eration, or maintenance of overhead supply and communication lines and their associated equipment. 

201. Scope 

Part 2 of this code covers supply and communication conductors and equipment in overhead lines. It 
covers the associated structural arrangements of such systems and the extension of such systems into 
buildings. The rules include requirements for spacing, clearances, and strength of construction. They 
do not cover installations in electric supply stations except as required by Rule 162A. 
NOTE 1: Part 4 contains the approach distances and work rules required of supply and communciation employ- 
ers and their employees working on or near supply and communication lines and equipment. 
NOTE 2: The approach distances to energized parts, and other requirements applicable to the activities of utility 
or non-utility construction personnel, and others in close proximity to existing supply lines are governed by the 
Occupational Health and Safety Administration (OSHA), federal, state, or local statutes or regulations. 

202. Application of Rules 

The general requirements for application of these rules are contained in Rule 013. However, when a 
structure is replaced, the arrangement of equipment shall conform to the current edition of Rule 238C. 



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210 PART 2. SAFETY RULES FOR OVERHEAD LINES 214B3 

Section 21. 
General Requirements 

210. Referenced Sections 

The Introduction (Section 1), Definitions (Section 2), References (Section 3), and Grounding Meth- 
ods (Section 9) shall apply to the requirements of Part 2. 

211. Number 211 not used in this edition. 

212. Induced Voltages 

Rules covering supply-line influence and communication-line susceptiveness have not been detailed in 
this code. Cooperative procedures are recommended in the control of voltages induced from proximate 
facilities. Therefore, reasonable advance notice should be given to owners or operators of other prox- 
imate facilities that may be adversely affected by new construction or changes in existing facilities. 

213. Accessibility 

All parts that must be examined or adjusted during operation shall be arranged so as to be accessible 
to authorized persons by the provision of adequate climbing spaces, working spaces, working facili- 
ties, and clearances between conductors. 

214. Inspection and Tests of Lines and Equipment 

A. When In Service 

1 . Initial Compliance With Rules 

Lines and equipment shall comply with these safety rules when placed in service. 

2. Inspection 

Lines and equipment shall be inspected at such intervals as experience has shown to be necessary. 

NOTE: It is recognized that inspections may be performed in a separate operation or while performing other 
duties, as desired. 

3. Tests 

When considered necessary , lines and equipment shall be subjected to practical tests to determine 
required maintenance. 

4. Record of Defects 

Any defects affecting compliance with this code revealed by inspection or tests, if not promptly 
corrected, shall be recorded; such records shall be maintained until the defects are corrected. 

5. Remedying Defects 

Lines and equipment with recorded defects that could reasonably be expected to endanger life or 
property shall be promptly repaired, disconnected, or isolated. 

B. When Out of Service 

1 . Lines Infrequently Used 

Lines and equipment infrequently used shall be inspected or tested as necessary before being 
placed into service. 

2. Lines Temporarily Out of Service 

Lines and equipment temporarily out of service shall be maintained in a safe condition. 

3. Lines Permanently Abandoned 

Lines and equipment permanently abandoned shall be removed or maintained in a safe condition. 

60 
Copyright © 2001 IEEE. All rights reserved. 



215 PART 2. SAFETY RULES FOR OVERHEAD LFNES 215C3 



215. Grounding of Circuits, Supporting Structures, and Equipment 

A. Methods 

Grounding required by these rules shall be in accordance with the applicable methods given in 
Section 9. 

B. Circuits 

1 . Common Neutral 

A conductor used as a common neutral for primary and secondary circuits shall be effectively 
grounded as specified in Section 9. 

2. Other Neutrals 

Primary line, secondary line, and service neutral conductors shall be grounded as specified in 

Section 9. 

EXCEPTION: Circuits designed for ground-fault detection and impedance-current-limiting devices. 

3. Other Conductors 

Line or service conductors, other than neutral conductors, that are intentionally grounded, shall be 
grounded as specified in Section 9. 

4. Surge Arresters 

Where the operation of surge arresters is dependent upon grounding, they shall be grounded in ac- 
cordance with the methods outlined in Section 9. 

5 . Use of Earth as Part of Circuit 

a. Supply circuits shall not be designed to use the earth normally as the sole conductor for any 
part of the circuit. 

b. Monopolar operation of a bipolar HVDC system is permissible for emergencies and limited 
periods for maintenance. 

C. Non-Current-Carrying Parts 

1 . General 

Metal or metal-reinforced supporting structures, including lamp posts; metal conduits and race- 
ways; cable sheaths; messengers; metal frames, cases, and hangers of equipment; and metal switch 
handles and operating rods shall be effectively grounded. 

EXCEPTION 1 : This rule does not apply to frames , cases , and hangers of equipment and switch handles and 
operating rods that are 2.45 m (8 ft) or more above readily accessible surfaces or are otherwise isolated or 
guarded and where the practice of not grounding such items has been a uniform practice over a well-defined 
area. 

EXCEPTION 2: This rule does not apply to isolated or guarded equipment cases in certain specialized 
applications, such as series capacitors where it is necessary that equipment cases be either ungrounded or 
connected to the circuit. Such equipment cases shall be considered as energized and shall be suitably 
identified. 

EXCEPTION 3: This rule does not apply to equipment cases, frames, equipment hangers, conduits, messen- 
gers, raceways, and cable sheaths enclosing or supporting only communication conductors, provided they are 
not exposed to contact with open supply conductors of over 300 V. 

2. Guys 

Guys shall be effectively grounded if attached to a supporting structure carrying any supply con- 
ductor of more than 300 V or if vulnerable to accidental energization by such conductors due to a 
slack conductor or guy. 

EXCEPTION 1: This rule does not apply to guys containing an insulator or insulators installed in accordance 
with and meeting the requirements of Rule 279 A. 

EXCEPTION 2: This rule does not apply to guys attached to supporting structures if all supply conductors 
are in cable conforming to the requirements of Rules 230C1, 230C2, or 230C3. 

EXCEPTION 3: This rule does not apply if the guy is attached to a supporting structure on private right-of- 
way if all the supply circuits exceeding 300 V meet the requirements of Rule 220B2. 

3. Multiple Messengers on the Same Structure 

Communication cable messengers exposed to power contacts, power induction, or lightning, shall 
be bonded together at intervals specified in Rule 92C. 

61 

Copyright © 2001 IEEE. All rights reserved. 






216 PART 2. SAFETY RULES FOR OVERHEAD LINES 217A2b 



216. Arrangement of Switches 

A. Accessibility 

Switches or their control mechanisms shall be installed so as to be accessible to authorized persons. 

B . Indicating Open or Closed Position 

Switch position shall be visible or clearly indicated. 

C. Locking 

Switch-operating mechanisms that are accessible to unauthorized persons shall have provisions for 
locking in each operational position. 

D. Uniform Position 

The handles or control mechanisms for all switches throughout any system should have consistent po- 
sitions when opened and uniformly different positions when closed in order to minimize operating er- 
rors. Where this practice is not followed, the switches should be marked to minimize mistakes in 
operation. 

E. Remotely controlled, automatic transmission, or distribution overhead line switching devices shall 
have local provisions to render remote or automatic controls inoperable. 

217. General 

A. Supporting Structures 

1 . Protection of Structures 

a. Mechanical Damage 

Appropriate physical protection shall be provided for supporting structures subject to vehicu- 
lar traffic abrasion that would materially affect their strength. 

NOTE: Nothing in this rule is intended to require protection or marking of structural components located 
outside of the traveled ways of roadways or established parking areas. Experience has shown that it is 
not practical to protect structures from contact by out-of-control vehicles operating outside of established 
traveled ways. 

b. Fire 

Supporting structures shall be placed and maintained so as to be exposed as little as is practical 
to brush, grass, rubbish, or building fires. 

c. Attached to Bridges 

Supporting structures attached to bridges for the purpose of carrying open supply conductors 
exceeding 600 V shall be posted with appropriate safety signs. 

NOTE: ANSI Z535.1-1998, ANSI Z535.2-1998, ANSI Z535.3-1998, ANSI Z535.4-1998, and ANSI 
Z535.5-1998 contain information regarding safety signs. 

2. Readily Climbable Supporting Structures 

a. Readily climbable supporting structures, such as closely latticed poles, towers, or bridge at- 
tachments, carrying open supply conductors energized at more than 300 V, which are adjacent 
to roads, regularly traveled pedestrian thoroughfares, or places where persons frequently gath- 
er (such as schools or public playgrounds), shall be equipped with barriers to inhibit climbing 
by unqualified persons or posted with appropriate safety signs. 

EXCEPTION: This rule does not apply where access to the supporting structure is limited by a fence 
meeting the height requirements of Rule 1 10 A 1 . 

NOTE: ANSI Z535.1-1998, ANSI Z535.2-1998, ANSI Z535.3-1998, ANSI Z535.4-1998, and ANSI 
Z535.5-1998 contain information regarding safety signs. 

b. Steps 

Steps permanently installed on supporting structures shall not be closer than 2.45 m (8 ft) from 

the ground or other accessible surface. 

EXCEPTION 1 : This rule does not apply where supporting structures are isolated. 

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217A2c PART 2. SAFETY RULES FOR OVERHEAD LINES 218B 



EXCEPTION 2: This rule does not apply where access to the supporting structure is limited by a fence 
meeting the height requirements of Rule 1 10A1 . 
c. Standoff Brackets 

Standoff brackets on supporting structures shall be arranged so that there is not less than 
2.45 m (8 ft) between either: 

(1) The lowest bracket and ground or other accessible surface, or 

(2) The two lowest brackets. 

EXCEPTION: This rule does not apply where supporting structures are isolated. 

3. Identification 

Supporting structures, including those on bridges, on which supply or communication conductors 
are maintained shall be so constructed, located, marked, or numbered so as to facilitate identifica- 
tion by employees authorized to work thereon. 

4. Obstructions 

Signs, posters, notices, and other attachments shall not be placed on supporting structures without 
concurrence of the owner. Supporting structures should be kept free from other climbing hazards 
such as tacks, nails, vines, and through bolts not properly trimmed. 

5. Decorative Lighting 

Attachment of decorative lighting on structures shall not be made without the concurrence of the 
owners and occupants. 

B. Unusual Conductor Supports 

Where line conductors are attached to structures other than those used solely or principally for their 
support, all rules shall be complied with as far as they apply. Such additional precautions as may be 
deemed necessary by the administrative authority shall be taken to avoid damage to the structures or 
injury to the persons using them. The supporting of conductors on trees and roofs should be avoided. 

218. Tree Trimming 

A. General 

1 . Trees that may interfere with ungrounded supply conductors should be trimmed or removed. 
NOTE: Normal tree growth, the combined movement of trees and conductors under adverse weather condi- 
tions, voltage, and sagging of conductors at elevated temperatures are among the factors to be considered in 
determining the extent of trimming required. 

2. Where trimming or removal is not practical, the conductor should be separated from the tree with 
suitable materials or devices to avoid conductor damage by abrasion and grounding of the circuit 
through the tree. 

B . At Line Crossings, Railroad Crossings, and Limited- Access Highway Crossings 

The crossing span and the adjoining span on each side of the crossing should be kept free from over- 
hanging or decayed trees or limbs that otherwise might fall into the line. 



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220 PART 2. SAFETY RULES FOR OVERHEAD LINES 220B2e 

Section 22. 

Relations Between Various 

Classes of Lines and Equipment 

220. Relative Levels 

A. Standardization of Levels 

The levels at which different classes of conductors are to be located should be standardized by agree- 
ment of the utilities concerned. 

B. Relative Levels: Supply and Communication Conductors 

1. Preferred Levels 

Where supply and communication conductors cross each other or are located on the same struc- 
tures, the supply conductors should be carried at the higher level. 

EXCEPTION: This rule does not apply to trolley feeders, which may be located for convenience approxi- 
mately at the level of the trolley-contact conductor. 

2. Special Construction for Supply Circuits, the Voltage of Which Is 600 V or Less and Carrying 
Power Not in Excess of 5 kW 

Where all circuits are owned or operated by one party or where cooperative consideration 
determines that the circumstances warrant and the necessary coordinating methods are employed, 
single-phase ac or two-wire dc circuits carrying a voltage of 600 V or less between conductors, 
with transmitted power not in excess of 5 kW, when involved in the joint use of structures with 
communication circuits, may be installed in accordance with footnote 1 of Table 235-5, under the 
following conditions: 

a. That such supply circuits are of covered conductor not smaller than AWG No. 8 medium 
hard-drawn copper or its equivalent in strength, and the construction otherwise conforms with 
the requirements for supply circuits of the same class. 

b. That the supply circuits be placed on the end and adjacent pins of the lowest through signal 
support arm and that a 750 mm (30 in) climbing space be maintained from the ground up to 
a point at least 600 mm (24 in) above the supply circuits. The supply circuits shall be rendered 
conspicuous by the use of insulators of different form or color from others on the pole line or 
by stenciling the voltage on each side of the support arm between the pins carrying each sup- 
ply circuit, or by indicating the voltage by means of metal characters. 

c. That there shall be a vertical clearance of at least 600 mm (2 ft) between the support arm car- 
rying these supply circuits and the next support arm above. The other pins on the support arm 
carrying the supply circuits may be occupied by communication circuits used in the operation 
or control of signal system or other supply system if owned, operated, and maintained by the 
same company operating the supply circuits. 

d. That such supply circuits shall be equipped with arresters and fuses installed in the supply end 
of the circuit and where the signal circuit is ac, the protection shall be installed on the 
secondary side of the supply transformer. The arresters shall be designed so as to break down 
at approximately twice the voltage between the wires of the circuit, but the breakdown voltage 
of the arrester need not be less than 1 kV. The fuses shall have a rating not in excess of 
approximately twice the maximum operating current of the circuit, but their rating need not 
be less than 10 A. The fuses likewise in all cases shall have a rating of at least 600 V, and 
where the supply transformer is a step-down transformer, shall be capable of opening the 
circuit successfully in the event the transformer primary voltage is impressed upon them. 

e. Such supply circuits in cable meeting the requirements of Rules 230C1, 230C2, or 230C3 may 
| be installed below communication attachments, with not less than 400 mm (16 in) vertical 

separation between the supply cable and the lowest communication attachment. 
Communication circuits other than those used in connection with the operation of the supply 
circuits shall not be carried in the same cable with such supply circuits. 

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220B2f PART 2. SAFETY RULES FOR OVERHEAD LINES 222 



f. Where such supply conductors are carried below communication conductors, transformers 
and other apparatus associated therewith shall be attached only to the sides of the support arm 
in the space between and at no higher level than such supply wires. 

g. Lateral runs of such supply circuits carried in a position below the communication space shall 
be protected through the climbing space by wood molding or equivalent covering, or shall be 
carried in insulated multiple-conductor cable, and such lateral runs shall be placed on the un- 
derside of the support arm. 

C. Relative Levels: Supply Lines of Different Voltage Classifications (as classified in Table 235-5) 

1 . At Crossings or Conflicts 

Where supply conductors of different voltage classifications cross each other or structure conflict 
exists, the higher- voltage lines should be carried at the higher level. 

2. On Structures Used Only by Supply Conductors 

Where supply conductors of different voltage classifications are on the same structures, relative 
levels should be as follows: 

a. Where all circuits are owned by one utility, the conductors of higher voltage should be placed 
above those of lower voltage. 

b. Where different circuits are owned by separate utilities, the circuits of each utility may be 
grouped together, and one group of circuits may be placed above the other group provided 
that the circuits in each group are located so that those of higher voltage are at the higher lev- 
els and that any of the following conditions is met: 

(1) A vertical spacing of not less than that required by Table 235-5 is maintained between 
the nearest line conductors of the respective utilities. 

(2) Conductors of a lower voltage classification placed at a higher level than those of a higher 
classification shall be placed on the opposite side of the structure. 

(3) Ownership and voltage are prominently displayed. 

D. Identification of Overhead Conductors 

All conductors of electric supply and communication lines should, as far as is practical, be arranged 
to occupy uniform positions throughout, or shall be constructed, located, marked, numbered, or at- 
tached to distinctive insulators or crossarms, so as to facilitate identification by employees authorized 
to work thereon. This does not prohibit systematic transposition of conductors. 

E. Identification of Equipment on Supporting Structures 

All equipment of electric supply and communication lines should be arranged to occupy uniform 
positions throughout or shall be constructed, located, marked, or numbered so as to facilitate 
identification by employees authorized to work thereon. 

221. Avoidance of Conflict 

Two separate lines, either of which carries supply conductors, should be so separated from each other 
that neither conflicts with the other. If this is not practical, the conflicting line or lines should be sep- 
arated as far as practical and shall be built to the grade of construction required by Section 24 for a 
conflicting line, or the two lines shall be combined on the same structures. 

222. Joint Use of Structures 

Joint use of structures should be considered for circuits along highways, roads, streets, and alleys. 
The choice between joint use of structures and separate lines shall be determined through cooperative 
consideration of all the factors involved, including the character of circuits, the total number and 
weight of conductors, tree conditions, number and location of branches and service drops, structure 
conflicts, availability of right-of-way, etc. Where such joint use is mutually agreed upon, it shall be 
subject to the appropriate grade of construction specified in Section 24. 

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223 PART 2. SAFETY RULES FOR OVERHEAD LINES 224A3c 



223. Communications Protective Requirements 

A. Where Required 

Where communication apparatus is handled by other than qualified persons, it shall be protected by 
one or more of the means listed in Rule 223B if such apparatus is permanently connected to lines sub- 
ject to any of the following: 

1. Lightning 

2. Contact with supply conductors whose voltage to ground exceeds 300 V 

3. Transient rise in ground potential exceeding 300 V 

4. Steady-state induced voltage of a hazardous level 

NOTE: When communication cables will be in the vicinity of supply stations where large ground currents 
may flow, the effect of these currents on communication circuits should be evaluated. 

B. Means of Protection 

Where communication apparatus is required to be protected under Rule 223A, protective means ad- 
equate to withstand the voltage expected to be impressed shall be provided by insulation, protected 
where necessary by surge arresters used in conjunction with fusible elements. Severe conditions may 
require the use of additional devices such as auxiliary arresters, drainage coils, neutralizing trans- 
formers, or isolating devices. 

224. Communication Circuits Located Within the Supply Space and Supply Circuits 
Located Within the Communication Space 

A. Communication Circuits Located in the Supply Space 

1 . Communication circuits located in the supply space shall be installed and maintained only by per- 
sonnel authorized and qualified to work in the supply space in accordance with the applicable 
rules of Sections 42 and 44. 

2. Communication circuits located in the supply space shall meet the following clearance require- 
ments, as applicable: 

a. Insulated communication cables supported by an effectively grounded messenger shall have 
the same clearances as neutrals meeting Rule 230E1 from communication circuits located in 
the communication space and from supply conductors located in the supply space. See Rules 
235 and 238. 

b. Fiber-optic cables located in the supply space shall meet the requirements of Rule 230F. 

c. Open- wire communication circuits permitted by other rules to be in the supply space shall 
have the same clearances from communication circuits located in the communication space 
and from other circuits located in the supply space as required by Rule 235 for open supply 
conductors of 0-750 V. 

EXCEPTION: Service drops meeting Rule 224A3a and 224A3b may originate in the supply space on a 
line structure or in the span and terminate in the communication space on the building or structure being 
served. 

3. Communication circuits located in the supply space in one portion of the system may be located 
in the communication space in another portion of the system if the following requirements are 
met: 

a. Where the communication circuit is, at any point, located above an energized supply conduc- 
tor or cable, the communication circuit shall be protected by fuseless surge arresters, drainage 
coils, or other suitable devices to limit the normal communication circuit voltage to 400 V or 
less to ground. 

NOTE: The grades of construction for communication conductors with inverted levels apply. 

b. Where the communication circuit is always located below the supply conductors, the commu- 
nication protection shall meet the requirements of Rule 223. 

c. The transition(s) between the supply space and the communication space shall occur on a sin- 
gle structure; no transition shall occur between line structures. 

EXCEPTION: Service drops meeting Rule 224A3a and Rule 224A3b may originate in the supply space 

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224A3d PART 2. SAFETY RULES FOR OVERHEAD LINES 225D2 



on a line structure or in the span and terminate in the communication space on the building or structure 
being served, 
d. The construction and protection shall be consistently followed throughout the extent of such 
section of the communications system. 

B. Supply Circuits Used Exclusively in the Operation of Communication Circuits 

Circuits used for supplying power solely to apparatus forming part of a communications system shall 
be installed as follows: 

1. Open-wire circuits shall have the grades of construction, clearances, insulation, etc., prescribed 
elsewhere in these rules for supply or communication circuits of the voltage concerned. 

2. Special circuits operating at voltages in excess of 90 V ac or 150 V dc and used for supplying 
power solely to communications equipment may be included in communication cables under the 
following conditions: 

a. Such cables shall have a conductive sheath or shield that is effectively grounded, and each 
such circuit shall be carried on conductors that are individually enclosed with an effectively 
grounded shield. 

b. All circuits in such cables shall be owned or operated by one party and shall be maintained 
only by qualified personnel. 

c. Supply circuits included in such cables shall be terminated at points accessible only to quali- 
fied personnel. 

d. Communication circuits brought out of such cables, if they do not terminate in a repeater sta- 
tion or terminal office, shall be protected or arranged so that in the event of failure within the 
cable, the voltage on the communication circuit will not exceed 400 V to ground. 

e. Terminal apparatus for the power supply shall be so arranged that the live parts are inacces- 
sible when such supply circuits are energized. 

EXCEPTION: The requirements of Rule 224B2 do not apply to communication circuits where the transmit- 
ted power does not exceed 150 W. 

225. Electric Railway Construction 

A. Trolley-Contact Conductor Fastenings 

All overhead trolley-contact conductors shall be supported and arranged so that the breaking of a sin- 
gle contact conductor fastening will not allow the trolley conductor live span wire, or current-carry- 
ing connection, to come within 3.0 m (10 ft) (measured vertically) from the ground, or from any 
platform accessible to the general public. 

Span-wire insulation for trolley-contact conductors shall comply with Rule 279B. 

B. High- Voltage Contact Conductors 

Trolley-contact conductors energized at more than 750 V shall be suspended in such a way that, if 
broken at one point, the conductor will not come within 3.6 m (12 ft) (measured vertically) of the 
ground, or any platform accessible to the public. 

C. Third Rails 

Third rails shall be protected by adequate guards composed of wood or other suitable insulating 

material. 

EXCEPTION: This rule does not apply where third rails are on fenced right-of-way. 

D. Prevention of Loss of Contact at Railroad Crossings at Grade 

At crossings at grade with other railroads or other electrified railway systems, contact conductors 
shall be arranged as set forth in the following specifications, 1, 2, 3, 4, and 5, following, whichever 
apply: 

1. Where the crossing span exceeds 30 m (100 ft), catenary construction shall be used for overhead 
trolley-contact conductors. 

2. When pole trolleys, using either wheels or sliding shoes, are used: 

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225D2a PART 2. SAFETY RULES FOR OVERHEAD LINES 225E 



a. The trolley-contact conductor shall be provided with live trolley guards of suitable construc- 
tion; or 

b. The trolley-contact conductor should be at a uniform height above its own track throughout 
the crossing span and the next adjoining spans. Where it is not practical to maintain a uniform 
height, the change in height shall be made in a gradual manner. 

EXCEPTION: Rule 225D2 does not apply where the crossing is protected by signals or interlocking. 

3. When collectors of the pantograph type are used, the contact conductor and track through the 
crossing should be maintained in a condition where the rocking of pantograph-equipped cars or 
locomotives will not de-wire the pantograph. If this cannot be done, auxiliary contact conductors 
shall be installed. Wire height shall conform with Rule 225D2. 

4. Where two electrified tracks cross: 

a. When the trolley-contact conductors are energized from different supply circuits, or from dif- 
ferent phases of the same circuit, the trolley-conductor crossover shall be designed to insulate 
both conductors from each other. The design shall not permit either trolley collector to contact 
any conductor or part energized at a different voltage than at which it is designed to operate. 

b. Trolley-contact crossovers used to insulate trolley conductors of the same voltage but of 
different circuit sections shall be designed to limit the likelihood of both sections being 
simultaneously contacted by the trolley collector. 

5. When third rail construction is used, and the length of the third rail gap at the crossings is such 
that a car or locomotive stopping on the crossing can lose propulsion power, the crossing shall be 
protected by signals or interlocking. 

Guards Under Bridges 

Trolley guards of suitable construction shall be provided where the trolley-contact conductor is so 
located that a trolley pole leaving the conductor can make simultaneous contact between it and the 
bridge structure. 



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230 PART 2. SAFETY RULES FOR OVERHEAD LINES 230Cla 



Section 23. 
Clearances 

230. General 

A. Application 

This section covers all clearances, including climbing spaces, involving overhead supply and commu- 
nication lines. 

NOTE: The more than 70 years of historical development and specification of clearances in Rules 232, 233, and 
234 were reviewed for consistency among themselves and with modern practice and were appropriately revised 
in both concept and content for the 1990 Edition. See Appendix A. 

1 . Permanent and Temporary Installations 

The clearances of Section 23 are required for permanent and temporary installations. 

2. Emergency Installations 

The clearances required in Section 23 may be decreased for emergency installations if the follow- 
ing conditions are met. 
NOTE: See Rule 014. 

a. Open supply conductors of to 750 V and supply cables meeting Rule 230C; and communi- 
cation conductors and cables, guys, messengers, and neutral conductors meeting Rule 230E1 
shall be suspended not less than 4.8 m (15.5 ft) above areas where trucks are expected, or 
2.70 m (9 ft) above areas limited to pedestrians or restricted traffic only where vehicles are not 
expected during the emergency, unless Section 23 permits lesser clearances. 

For the purpose of this rule, trucks are defined as any vehicle exceeding 2.5 m (8 ft) in 
height. Areas not subject to truck traffic are areas where truck traffic is neither normally en- 
countered nor reasonably anticipated or is otherwise limited. 

Spaces and ways subject to pedestrians or restricted traffic only are those areas where 
riders on horseback, vehicles, or other mobile units exceeding 2.5 m (8 ft) in height are 
prohibited by regulation or permanent terrain configurations or are otherwise neither normally 
encountered nor reasonably anticipated or are otherwise limited. 

b. Vertical clearances of open supply conductors above 750 V shall be increased above the 
applicable value of Rule 230A2a as appropriate for the voltage involved and the given local 
conditions. 

c. Reductions in horizontal clearances permitted by this rule shall be in accordance with accepted 
good practice for the given local conditions during the term of the emergency. 

d. Supply and communication cables may be laid directly on grade if they are guarded or 
otherwise located so that they do not unduly obstruct pedestrian or vehicular traffic and are 
appropriately marked. Supply cables operating above 600 V shall meet either Rule 230C or 
Rule350B. 

e. No clearance is specified for areas where access is limited to qualified personnel only. 

B . Measurement of Clearance and Spacing 

Unless otherwise stated, all clearances shall be measured from surface to surface and all spacings shall 
be measured center to center. For clearance measurement, live metallic hardware electrically connect- 
ed to line conductors shall be considered a part of the line conductors. Metallic bases of potheads, 
surge arresters, and similar devices shall be considered a part of the supporting structure. 

C. Supply Cables 

For clearance purposes, supply cables, including splices and taps, conforming to any of the following 
requirements are permitted lesser clearances than open conductors of the same voltage. Cables should 
be capable of withstanding tests applied in accordance with an applicable standard. 
1 . Cables that are supported on or cabled together with an effectively grounded bare messenger or 
neutral, or with multiple concentric neutral conductors, where any associated neutral conductor(s) 
meet(s) the requirements of Rule 230E1 and where the cables also meet one of the following: 
a. Cables of any voltage having an effectively grounded continuous metal sheath or shield, or 

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I 



230Clb PART 2. SAFETY RULES FOR OVERHEAD LINES 230H 



b. Cables designed to operate on a multi-grounded system at 22 kV or less and having semicon- 
ducting insulation shielding in combination with suitable metallic drainage. 

2. Cables of any voltage, not included in Rule 230C1, covered with a continuous auxiliary 
semiconducting shield in combination with suitable metallic drainage and supported on and 
cabled together with an effectively grounded bare messenger. 

3 . Insulated, nonshielded cable operated at not over 5 kV phase to phase, or 2.9 kV phase to ground, 
supported on and cabled together with an effectively grounded bare messenger. 

D. Covered Conductors 

Covered conductors shall be considered bare conductors for all clearance requirements except that 
spacing between conductors of the same or different circuits, including grounded conductors, may be 
reduced below the requirements for open conductors when the conductors are owned, operated, or 
maintained by the same party and when the conductor covering provides sufficient dielectric strength 
to limit the likelihood of a short circuit in case of momentary contact between conductors or between 
conductors and the grounded conductor. Intermediate spacers may be used to maintain conductor 
spacing and to provide support. 

E. Neutral Conductors 

1 . Neutral conductors that are effectively grounded throughout their length and associated with cir- 
cuits of to 22 kV to ground may have the same clearances as guys and messengers. 

2. All other neutral conductors of supply circuits shall have the same clearances as the phase con- 
ductors of the circuit with which they are associated. 

F. Fiber-Optic Cable 

1 . Fiber-optic — supply cable 

a. Cable defined as "fiber-optic— supply" supported on a messenger that is effectively grounded 
throughout its length shall have the same clearance from communications facilities as required 
for a neutral conductor meeting Rule 230E1 . 

b. Cable defined as "fiber-optic— supply" that is entirely dielectric, or supported on a messenger 
that is entirely dielectric, shall have the same clearance from communications facilities as re- 
quired for a neutral conductor meeting Rule 230E1 . 

c. Fiber-optic— supply cables supported on or within messengers not meeting Rule 230Fla or 
230Flb shall have the same clearances from communications facilities required for such 
messengers. 

d. Fiber-optic — supply cables supported on or within a conductor(s), or containing a conduc- 
tors) or cable sheath(s) within the fiber-optic cable assembly shall have the same clearances 
from communications facilities required for such conductors. Such clearance shall be not less 
than that required under Rule 230Fla, 230Flb, or 230Flc, as applicable. 

e. Fiber-optic— supply cables meeting Rule 224 A3 are considered to be communication cables 
when located in the communication space. 

2. Fiber-optic— communication cable 

Cable defined as "fiber-optic— communication" shall have the same clearance from supply facil- 
ities as required for a communication messenger. 

G. Alternating- and Direct-Current Circuits 

The rules of this section are applicable to both ac and dc circuits. For dc circuits, the clearance re- 
quirements shall be the same as those for ac circuits having the same crest voltage to ground. 
NOTE: Although the corresponding crest voltage for a common sinusoidal ac circuit may be calculated by 
multiplying its rms value by 1 .414 (square root of 2), this may not be appropriate for other type ac circuits. An 
example of the latter is represented by non-sinusoidal power supplies such as used in some coaxial cable type 
communication systems. 

H. Constant-Current Circuits 

The clearances for constant-current circuits (such as series lighting circuits) shall be determined on 
the basis of their normal full-load voltage. 

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2301 PART 2. SAFETY RULES FOR OVERHEAD LINES 232A1 



I. Maintenance of Clearances and Spacings 

The clearances and spacing required shall be maintained at the values and under the conditions spec- 
ified in Section 23 of the applicable edition. 
NOTE: See Rule 013 to determine the applicable edition. 

231. Clearances of Supporting Structures From Other Objects 

Supporting structures, support arms and equipment attached thereto, and braces shall have the follow- 
ing clearances from other objects. The clearance shall be measured between the nearest parts of the 
objects concerned. 

A. From Fire Hydrants 

Not less than 1 .2 m (4 ft). 

EXCEPTION: Where conditions do not permit, a clearance of not less than 900 mm (3 ft) is allowed. 

B. From Streets, Roads, and Highways 

1 . Where there are curbs: supporting structures, support arms, anchor guys, or equipment attached 
thereto, up to 4.6 m (15 ft) above the road surface shall be located a sufficient distance from the 
street side of the curbs to avoid contact by ordinary vehicles using and located on the traveled way. 
For a redirectional curb, such distance shall be not less than 150 mm (6 in). For paved or concrete 
swale-type curbs, such facilities shall be located behind the curb. 

2. Where there are no curbs, supporting structures should be located a sufficient distance from the 
roadway to avoid contact by ordinary vehicles using and located on the traveled way. 

3. Location of overhead utility installations on highways with narrow rights-of-way or on urban 
streets with closely abutting improvements are special cases that must be resolved in a manner 
consistent with the prevailing limitations and conditions. 

4 . Where a governmental authority exercising jurisdiction over structure location has issued a permit 
for, or otherwise approved, specific locations for supporting structures, that permit or approval 
shall govern. 

C. From Railroad Tracks 

Where railroad tracks are parallel to or crossed by overhead lines, all portions of the supporting struc- 
tures, support arms, anchor guys, and equipment attached thereto less than 6.7 m (22 ft) above the 
nearest track rail shall have horizontal clearances not less than the values required by Rule 231 CI or 
Rule 231C2 for the situation concerned. 
NOTE: See Rule 2341. 

1 . Not less than 3 .6 m ( 1 2 ft) from the nearest track rail . 

EXCEPTION 1: A clearance of not less than 2.13 m (7 ft) may be allowed where the supporting structure is 
not the controlling obstruction, provided sufficient space for a driveway is left where cars are loaded or un- 
loaded. 

EXCEPTION 2: Supports for overhead trolley-contact conductors may be located as near their own track rail 
as conditions require. If very close, however, permanent screens on cars will be necessary to protect 
passengers. 

EXCEPTION 3: Where necessary to provide safe operating conditions that require an uninterrupted view of 
signals, signs, etc., along tracks, the parties concerned shall cooperate in locating structures to provide the 
necessary clearance. 

EXCEPTION 4: At industrial sidings, a clearance of not less than 2.13 m (7 ft) shall be permitted, provided 
sufficient space is left where cars can be loaded or unloaded. 

2. The clearances of Rule 231C1 may be reduced by agreement with the railroad(s). 

232. Vertical Clearances of Wires, Conductors, Cables, and Equipment Above Ground, 
Roadway, Rail, or Water Surfaces 

A. Application 

The vertical clearances specified in Rule 232B 1 apply under the following conductor temperature and 
loading conditions, whichever produces the largest final sag. 
1. 50 °C (120 °F), no wind displacement. 

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232A2 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



232Clb 



2. The maximum conductor temperature for which the line is designed to operate, if greater than 
50 °C (120 °F), with no wind displacement. 

3. °C (32 °F), no wind displacement, with radial thickness of ice, if any, specified in Rule 250B 
for the loading district concerned. 

EXCEPTION: The conductor temperature and loading condition for trolley and electrified railroad contact 
conductors shall be 15 °C (60 °F), no wind displacement, final unloaded sag, or initial unloaded sag in cases 
where these facilities are maintained approximately at initial unloaded sags. 

NOTE: The phase and neutral conductors of a supply line are normally considered separately when deter- 
mining the sag of each due to temperature rise. 



B. Clearance of Wires, Conductors, Cables, Equipment, and Support Arms Mounted on Supporting 
Structures 

1 . Clearance to Wires , Conductors , and Cables 

The vertical clearance of wires, conductors, and cables above ground in generally accessible plac- 
es, roadway, rail, or water surfaces, shall be not less than that shown in Table 232-1 . 

2. Clearance to Unguarded Rigid Live Parts of Equipment 

The vertical clearance above ground, roadway, or water surfaces for unguarded rigid live parts 
such as potheads, transformer bushings, surge arresters, and short lengths of supply conductors 
connected thereto, which are not subject to variation in sag, shall be not less than that shown in 
Table 232-2. For clearances of drip loops of service drops, see Table 232-1 . 

3. Clearance to Support Arms and Equipment Cases 

The vertical clearance of equipment cases , support arms , platforms , and braces that extend beyond 
the surface of the structure shall be not less than that shown in Table 232-2. These clearances do 
not apply to internal structural braces for latticed towers, X-braces between poles, and pole-type 
push braces. 

4. Street and Area Lighting 

a. The vertical clearance of street and area lighting luminaires shall be not less than that shown 
in Table 232-2. For this purpose, grounded luminaire cases and brackets shall be considered 
as effectively grounded equipment cases; ungrounded luminaire cases and brackets shall be 
considered as a rigid live part of the voltage contained. 

EXCEPTION: This rule does not apply to post-top mounted luminaires with grounded or entirely dielec- 
tric cases. 

b. Insulators, as specified in Rule 279A, should be inserted at least 2.45 m (8 ft) from the ground 
in metallic suspension ropes or chains supporting lighting units of series circuits. 



Additional Clearances for Wires, Conductors, Cables, and Unguarded Rigid Live Parts of Equipment 
Greater clearances than specified by Rule 232B shall be provided where required by Rule 232C1 . 
1 . Voltages Exceeding 22 kV 

a. For voltages between 22 and 470 kV, the clearance specified in Rule 232B1 (Table 232-1) or 
Rule 232B2 (Table 232-2) shall be increased at the rate of 10 mm (0.4 in) per kilovolt in ex- 
cess of 22 kV. For voltages exceeding 470 kV, the clearance shall be determined by the meth- 
od given in Rule 232D. All clearances for lines over 50 kV shall be based on the maximum 
operating voltage. 

EXCEPTION: For voltages exceeding 98 kV ac to ground or 139 kV dc to ground, clearances less than 
those required above are permitted for systems with known maximum switching-surge factors (see Rule 
232D). 

b. For voltages exceeding 50 kV, the additional clearance specified in Rule 232Cla shall be in- 
creased 3% for each 300 m (1000 ft) in excess of 1000 m (3300 ft) above mean sea level. 



72 
Copyright © 2001 IEEE. All rights reserved. 



232Clc PART 2. SAFETY RULES FOR OVERHEAD LINES 232D4 



c . For voltages exceeding 98 kV ac to ground, either the clearances shall be increased or the elec- 
tric field, or the effects thereof, shall be reduced by other means as required to limit the steady- 
state current due to electrostatic effects to 5 mA rms if the largest anticipated truck, vehicle, 
or equipment under the line were short-circuited to ground. The size of the anticipated truck, 
vehicle, or equipment used to determine these clearances may be less than but need not be 
greater than that limited by federal, state, or local regulations governing the area under the line. 
For this determination, the conductors shall be at a final unloaded sag at 50 °C (120 °F). 

D. Alternate Clearances for Voltages Exceeding 98 kV AC to Ground or 139 kV DC to Ground 

The clearances specified in Rules 232B and 232C may be reduced for circuits with known switching- 
surge factors, but shall be not less than the alternate clearance, which is computed by adding the 
reference height from Rule 232D2 to the electrical component of clearance from Rule 232D3. 

1 . Sag Conditions of Line Conductors 

The vertical clearance shall be maintained under the conductor temperature and loading condition 
given in Rule 232A. 

2. Reference Heights 

The reference height shall be selected from Table 232-3. 

3 . Electrical Component of Clearance 

a. The electrical component (D) shall be computed using the following equations. Selected val- 
ues of D are listed in Table 232-4. 

1.667 

be (m) 

1.667 

be (ft) 



maximum ac crest operating voltage to ground or maximum dc operating voltage 
to ground in kilo volts, 
PU = maximum switching-surge factor expressed in per-unit peak voltage to ground and 
defined as a switching-surge level for circuit breakers corresponding to 98% prob- 
ability that the maximum switching surge generated per breaker operation does not 
exceed this surge level, or the maximum anticipated switching-surge level gener- 
ated by other means, whichever is greater, 

a = 1 .15 , the allowance for three standard deviations, 

b = 1 .03 , the allowance for nonstandard atmospheric conditions , 

c = 1 .2, the margin of safety, 

K = 1 . 1 5 , the configuration factor for conductor-to-plane gap . 

b. The value of D shall be increased 3% for each 300 m (1000 ft) in excess of 450 m (1500 ft) 
above mean sea level. 

c . For voltages exceeding 98 kV ac to ground , either the clearances shall be increased or the elec- 
tric field, or the effects thereof, shall be reduced by other means as required to limit the steady 
state current due to electrostatic effects to 5 mA, rms, if the largest anticipated truck, vehicle, 
or equipment under the line were short-circuited to ground. The size of the anticipated truck, 
vehicle, or equipment used to determine these clearances may be less than but need not be 
greater than that limited by federal, state, or local regulations governing the area under the line. 
For this determination, the conductors shall be at a final unloaded sag at 50 °C (120 °F). 

Limit 

The alternate clearance shall be not less than the clearance given in Tables 232-1 or 232-2 com- 
puted for 98 kV ac to ground in accordance with Rule 232C. 



D = 1.00 


~V -(PU)-al 


500K 


D = 3.28 


rv ■ (PU) ■ en 
I 5Q0K J 


where 


V 


= maximum 



73 
Copyright © 2001 IEEE. All rights reserved. 



T-232-l(m) 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-232-l(m) 



m 



Table 232-1 

Vertical Clearance of Wires, Conductors, and Cables Above Ground, 

Roadway, Rail, or Water Surfaces 25 

(Voltages are phase to ground for effectively grounded circuits and those other circuits where all ground 

faults are cleared by promptly de-energizing the faulted section, both initially and following subsequent 

breaker operations. See the definitions section for voltages of other systems. 

See Rules 232B1 , 232Cla, and 232D4.) 



Nature of surface 

underneath wires, 

conductors, or cables 


Insulated 

communication 

conductors and 

cable; 

messengers; 

surge-protection 

wires; grounded 

guys; 

ungrounded 

guys exposed to 

to 300 V 11 ' 15 ; 

neutral 

conductors 

meeting Rule 

230E1; supply 

cables meeting 

Rule 230C1 

(m) 


Noninsulated 

communication 

conductors; 

supply cables 

of to 750 V 

meeting Rules 

230C2 or 

230C3 

(m) 


Supply cables 
over 750 V 

meeting 

Rules 230C2 

or 230C3; 

open supply 

conductors, 

to 750 V; 
ungrounded 
guys exposed 
to over 300 V 

to 750 V 14 

(m) 


Open supply 

conductors, 

over 750 V 

to 22 kV; 

ungrounded 

guys 

exposed to 

750 V to 

22 kV 14 
(m) 


Trolley and 

electrified railroad 

contact 

conductors and 

associated span or 

messenger wires 


Oto 
750 V 

to 
ground 

(m) 


Over 

750 V to 

22 kV 

to 

ground 

(m) 


Where wires, conductors, or cables cross over or overhang 


1 . Track rails of railroads 
(except electrified 
railroads using overhead 
trolley conductors) 2 ' 16 ' 

22 


7.2 


7.3 


7.5 


8.1 


6.7 4 


6.7 4 


2 . Roads , streets , and other 
areas subject to truck 
traffic 23 


4.7 


4.9 


5.0 


5.6 


5.5 5 


6.1 5 


3 . Driveways , parking lots , 
and alleys 


4. 7 7.13 


4. 9 7.13 


5.0 7 


5.6 


5.5 5 


6.1 5 


4. Other land traversed by 
vehicles, such as 
cultivated, grazing, 
forest, orchard, etc. 2 


4.7 


4.9 


5.0 


5.6 


- 


— 


5 . Spaces and ways subject 
to pedestrians or 
restricted traffic only 


2.9 


3.6 8 


3.8 8 


4.4 


4.9 


5.5 


6. Water areas not suitable 
for sailboating or where 
sailboating is 
prohibited 21 


4.0 


4.4 


4.6 


5.2 


— 


— 


7. Water areas suitable for 
sailboating including 
lakes, ponds, reservoirs, 
tidal waters, rivers, 
streams, and canals with 
an unobstructed surface 
area of 17 ' 18 - 19 ' 20 ' 21 














a. Less than 0.08 km 2 


5.3 


5.5 


5.6 


6.2 


— 


— 


b. Over 0.08 to 0.8 km 2 


7.8 


7.9 


8.1 


8.7 


— 


— 



74 
Copyright © 2001 IEEE. All rights reserved. 



T-232-l(m) 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-232-l(m) 



m 



Table 232-1 (Continued) 

Vertical Clearance of Wires, Conductors, and Cables Above Ground, 

Roadway, Rail, or Water Surfaces 2 

(Voltages are phase to ground for effectively grounded circuits and those other circuits where all ground 

faults are cleared by promptly de-energizing the faulted section, both initially and following subsequent 

breaker operations. See the definitions section for voltages of other systems. 

See Rules 232B1, 232Cla, and 232D4.) 



Nature of surface 

underneath wires, 

conductors, or cables 


Insulated 

communication 

conductors and 

cable; 

messengers; 

surge-protection 

wires; grounded 

guys; 

ungrounded 

guys exposed to 

to 300 V 11 ' 15 ; 

neutral 

conductors 

meeting Rule 

230E1; supply 

cables meeting 

Rule 230C1 

(m) 


Noninsulated 

communication 

conductors; 

supply cables 

of to 750 V 

meeting Rules 

230C2 or 

230C3 

(m) 


Supply cables 
over 750 V 

meeting 

Rules 230C2 

or 230C3; 

open supply 

conductors, 

to 750 V; 
ungrounded 
guys exposed 
to over 300 V 

to 750 V 14 

(m) 


Open supply 

conductors, 

over 750 V 

to22kV; 

ungrounded 

guys 

exposed to 

750 V to 

22 kV 14 

(m) 


Trolley and 

electrified railroad 

contact 

conductors and 

associated span or 

messenger wires 


Oto 
750 V 

to 
ground 

(m) 


Over 

750 V to 

22 kV 

to 

ground 

(m) 


c. Over 0.8 to 8 km 2 


9.6 


9.8 


9.9 


10.5 


— 


— 


d. Over 8 km 2 


11.4 


11.6 


11.7 


12.3 


— 


— 


8 . Established boat ramps 
and associated rigging 
areas; areas posted with 
sign(s) for rigging or 
launching sail boats 


Clearance above ground shall be 1 .5 m greater than in 7 above, 
for the type of water areas served by the launching sites 


Where wires, conductors, or cables run along and within the limits of 
highways or other road rights-of-way but do not overhang the roadway 


9 . Roads , streets , or alleys 


4.7 24 


4.9 


5.0 


5.6 


5.5 5 


6.1 5 


10. Roads in rural districts 
where it is unlikely that 
vehicles will be crossing 
under the line 


4 j 10, 12 


4.3 10 


4.4IO 


5.0 


5.5 5 


6.1 5 



I 



1 Where subways, tunnels, or bridges require it, less clearance above ground or rails than required by Table 
232-1 may be used locally. The trolley and electrified railroad contact conductor should be graded very grad- 
ually from the regular construction down to the reduced elevation. 

2 For wires, conductors, or cables crossing over mine, logging, and similar railways that handle only cars 
lower than standard freight cars, the clearance may be reduced by an amount equal to the difference in height 
between the highest loaded car handled and 6.1 m, but the clearance shall not be reduced below that required 
for street crossings. 

This footnote not used in this edition. 

In communities where 6.4 m has been established, this clearance may be continued if carefully main- 
tained. The elevation of the contact conductor should be the same in the crossing and next adjacent spans. 
(See Rule 225D2 for conditions that must be met where uniform height above rail is impractical.) 



75 
Copyright © 2001 IEEE. All rights reserved. 



T-232-l(m) PART 2. SAFETY RULES FOR OVERHEAD LINES T-232-l(m) 

In communities where 4.9 m has been established for trolley and electrified railroad contact conductors 
to 750 V to ground, or 5.5 m for trolley and electrified railroad contact conductors exceeding 750 V, or 
where local conditions make it impractical to obtain in the clearance given in the table, these reduced clear- 
ances may be used if carefully maintained. 
6 This footnote not used in this edition. 
Where the height of a building or other installation does not permit service drops to meet these values, 
the clearances over residential driveways only may be reduced to the following: 

(meters) 

(a) Insulated supply service drops limited to 

300 V to ground 3.8 

(b) Insulated drip loops of supply service drops limited to 300 V to ground 3.2 

(c) Supply service drops limited to 150 V to ground and meeting Rules 230C1 or 230C3 3.6 

(d) Drip loops only of service drops limited to 150 V to ground and meeting Rules 230C1 
or230C3 3.0 

(e) Insulated communication service drops 3.5 

Where the height of a building or other installation does not permit service drops to meet these values, 
the clearances may be reduced to the following: 

(meters) 

(a) Insulated supply service drops limited to 300 V to ground 3.2 

(b) Insulated drip loops of supply service drops limited to 300 V to ground 3.2 

(c) Supply service drops limited to 150 V to ground and meeting Rules 230C1 or 230C3 3.0 

(d) Drip loops only of supply service drops limited to 150 V to ground and meeting 

Rules 230C1 or230C3 3.0 

9 Spaces and ways subject to pedestrians or restricted traffic only are those areas where riders on horses or 
other large animals, vehicles, or other mobile units exceeding a total height of 2.45 m, are prohibited by 
regulation or permanent terrain configurations, or are otherwise not normally encountered nor reasonably 
anticipated. 

Where a supply or communication line along a road is located relative to fences, ditches, embankments, 
etc., so that the ground under the line would not be expected to be traveled except by pedestrians, the clear- 
ances may be reduced to the following values: 

(meters) 

(a) Insulated communication conductor and communication cables 2.9 

(b) Conductors of other communication circuits 2.9 

(c) Supply cables of any voltage meeting Rule 230C1 , supply cables limited to 150 V 

to ground meeting Rules 230C2 or 230C3, and neutral conductors meeting Rule 230E1 2.9 

(d) Insulated supply conductors limited to 300 V to ground 3.8 

(e) Guys 2.9 

11 No clearance from ground is required for anchor guys not crossing tracks, rails, streets, driveways, 
roads, or pathways. 

12 This clearance may be reduced to 4.0 m for communication conductors and guys. 

Where this construction crosses over or runs along alleys, driveways, or parking lots not subject to truck 
traffic this clearance may be reduced to 4.6 m. 

14 Ungrounded guys and ungrounded portions of span guys between guy insulators shall have clearances 
based on the highest voltage to which they may be exposed due to a slack conductor or guy. 

15 Anchor guys insulated in accordance with Rule 279 may have the same clearance as grounded guys. 

16 Adjacent to tunnels and overhead bridges that restrict the height of loaded rail cars to less than 6.1 m, 
these clearances may be reduced by the difference between the highest loaded rail car handled and 6.1 m, if 
mutually agreed to by the parties at interest. 

17 For controlled impoundments, the surface area and corresponding clearances shall be based upon the 
design high- water level. 



76 
Copyright © 2001 IEEE. All rights reserved. 



T-232-l(m) 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-232-l(ft) 



I 



I 



18 For uncontrolled water flow areas, the surface area shall be that enclosed by its annual high-water mark. 
Clearances shall be based on the normal flood level; if available, the 10-year flood level may be assumed as 
the normal flood level. 

The clearance over rivers, streams, and canals shall be based upon the largest surface area of any 1.6 
km-long segment that includes the crossing. The clearance over a canal, river, or stream normally used to 
provide access for sailboats to a larger body of water shall be the same as that required for the larger body of 
water. 

Where an overwater obstruction restricts vessel height to less than the applicable reference height given 
in Table 232-3, the required clearance may be reduced by the difference between the reference height and the 
overwater obstruction height, except that the reduced clearance shall be not less than that required for the sur- 
face area on the line-crossing side of the obstruction. 

Where the US Army Corps of Engineers, or the state, or surrogate thereof has issued a crossing permit, 
clearances of that permit shall govern. 



22 
23 



See Rule 2341 for the required horizontal and diagonal clearances to rail cars. 



For the purpose of this rule, trucks are defined as any vehicle exceeding 2.45 m in height. Areas not 
subject to truck traffic are areas where truck traffic is not normally encountered nor reasonably anticipated. 

Communication cables and conductors may have a clearance of 4.6 m where poles are back of curbs or 
other deterrents to vehicular traffic. 

The clearance values shown in this table are computed by adding the applicable Mechanical and Elec- 
trical (M & E) value of Table A-l to the applicable Reference Component of Table A-2a of Appendix A. 

When designing a line to accommodate oversized vehicles, these clearance values shall be increased by 
the difference between the known height of the oversized vehicle and 4.3 m. 



ft 



Table 232-1 



Vertical Clearance of Wires, Conductors, and Cables Above Ground, 
Roadway, Rail, or Water Surfaces 25 

(Voltages are phase to ground for effectively grounded circuits and those other circuits where all ground 

faults are cleared by promptly de-energizing the faulted section, both initially and following subsequent 

breaker operations. See the definitions section for voltages of other systems. 

See Rules 232B 1 , 232C 1 a, and 232D4 .) 



I 



Nature of surface 

underneath wires, 

conductors, or cables 


Insulated 
communication 
conductors and 
cable; messengers; 
surge-protection 
wires; grounded 

guys; 

ungrounded guys 

exposed to to 

300 V n > 15; 

neutral conductors 

meeting Rule 

230E1; supply 

cables meeting Rule 

230C1 

(ft) 


Noninsulated 
communication 

conductors; 
supply cables of 

to 750 V 

meeting Rules 

230C2 or 

230C3 

(ft) 


Supply 

cables over 

750 V 

meeting 
Rules 230C2 

or 230C3; 
open supply 
conductor s,0 

to 750 V; 
ungrounded 
guys exposed 
to over 300 V 

to 750 V 14 

(ft) 


Open 

supply 

conductors, 

over 750 V 

to 22 kV; 

ungrounded 

guys 

exposed to 

750 V to 

22 kV 14 

(ft) 


Trolley and 

electrified 

railroad contact 

conductors and 

associated span or 

messenger wires 


Oto 
750 V 

to 
ground 

(ft) 


Over 

750 V 
to 22 kV 

to 
ground 

(ft) 


Where wires, conductors, or cables cross over or overhang 


1 . Track rails of railroads 
(except electrified 
railroads using overhead 
trolley conductors) ' ' 


23.5 


24.0 


24.5 


26.5 


22.0 4 


22.0 4 


2. Roads, streets, and other 
areas subject to truck 

traffic 23 


15.5 


16.0 


16.5 


18.5 


18.0 5 


20.0 5 



77 
Copyright © 2001 IEEE. All rights reserved. 



T-232-l(ft) 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-232-l(ft) 



ft 



Table 232-1 (Continued) 

Vertical Clearance of Wires, Conductors, and Cables Above Ground, 

Roadway, Rail, or Water Surfaces 25 

(Voltages are phase to ground for effectively grounded circuits and those other circuits where all ground 

faults are cleared by promptly de-energizing the faulted section, both initially and following subsequent 

breaker operations. See the definitions section for voltages of other systems. 

See Rules 232B 1 , 232Cla, and 232D4.) 



Nature of surface 

underneath wires, 

conductors, or cables 


Insulated 
communication 
conductors and 
cable; messengers; 
surge-protection 
wires; grounded 

guys; 

ungrounded guys 

exposed to to 

300V 11,1S; 

neutral conductors 

meeting Rule 

230E1; supply 

cables meeting Rule 

230C1 

(ft) 


Noninsulated 
communication 

conductors; 
supply cables of 

to 750 V 

meeting Rules 

230C2 or 

230C3 

(ft) 


Supply 

cables over 

750 V 

meeting 

Rules 230C2 

or230C3; 

open supply 

conductors, 

to 750 V; 

ungrounded 

guys exposed 

to over 300 V 

to 750 V 14 

(ft) 


Open 

supply 

conductors, 

over 750 V 

to 22 kV; 

ungrounded 

guys 

exposed to 

750 V to 

22 kV 14 
(ft) 


Trolley and 

electrified 

railroad contact 

conductors and 

associated span or 

messenger wires 


Oto 
750 V 

to 
ground 

(ft) 


Over 

750 V 

to 22 kV 

to 

ground 

(ft) 


3 . Driveways, parking lots, 
and alleys 23 


15.5 7 ' 13 


16.0 7 ' 13 


16.5 7 


18.5 


18.0 5 


20 .0 5 


4. Other land traversed by 
vehicles, such as 
cultivated, grazing, 

forest, orchards, etc. 


15.5 


16.0 


16.5 


18.5 


— 


— 


5. Spaces and ways subject 
to pedestrians or 

restricted traffic only 


9.5 


12.0 8 


12. 5 8 


14.5 


16.0 


18.0 


6. Water areas not suitable 
for sailboating or where 
sailboating is 
prohibited 21 


14.0 


14.5 


15.0 


17.0 


- 


— 


7. Water areas suitable for 
sailboating including 
lakes, ponds, reservoirs, 
tidal waters, rivers, 
streams, and canals with 
an unobstructed surface 
area of 17 - 1M9.20.21 














a. Less than 20 acres 


17.5 


18.0 


18.5 


20.5 


- 


— 


b. Over 20 to 200 acres 


25.5 


26.0 


26.5 


28.5 


— 


— 


c. Over 200 to 2000 
acres 


31.5 


32.0 


32.5 


34.5 


— 


— 


d. Over 2000 acres 


37.5 


38.0 


38.5 


40.5 


— 


— 


8. Established boat ramps 
and associated rigging 
areas; areas posted with 
sign(s) for rigging or 
launching sail boats 


Clearance above ground shall be 5 ft greater than in 7 above, 
for the type of water areas served by the launching site 


Where wires, conductors, or cables run along and within the limits of highways 
or other road rights-of-way but do not overhang the roadway 


9. Roads, streets, or alleys 


15.5 24 


16.0 


16.5 


18.5 


18.0 5 


20 .0 5 


10. Roads in rural districts 
where it is unlikely that 
vehicles will be 
crossing under the line 


13.5 10 ' 12 


14.0 10 


14.5 10 


16.5 


18.0 5 


20.0 5 



78 
Copyright © 2001 IEEE. All rights reserved. 



T-232-l(ft) PART 2. SAFETY RULES FOR OVERHEAD LINES T-232-l(ft) 



I Where subways, tunnels, or bridges require it, less clearance above ground or rails than required by 
Table 232-1 may be used locally . The trolley and electrified railroad contact conductor should be graded very 
gradually from the regular construction down to the reduced elevation. 

For wires, conductors, or cables crossing over mine, logging, and similar railways that handle only cars 
lower than standard freight cars, the clearance may be reduced by an amount equal to the difference in height 
between the highest loaded car handled and 20 ft, but the clearance shall not be reduced below that required 
for street crossings. 

This footnote not used in this edition. 

In communities where 21 ft has been established, this clearance may be continued if carefully main- 
tained. The elevation of the contact conductor should be the same in the crossing and next adjacent spans. 
(See Rule 225D2 for conditions that must be met where uniform height above rail is impractical.) 

In communities where 16 ft has been established for trolley and electrified railroad contact conductors 
to 750 V to ground, or 18 ft for trolley and electrified railroad contact conductors exceeding 750 V, or where 
local conditions make it impractical to obtain the clearance given in the table, these reduced clearances may 
be used if carefully maintained. 

6 This footnote not used in this edition. 

7 Where the height of a building or other installation does not permit service drops to meet these values, 
the clearances over residential driveways only may be reduced to the following: 

(feet) 

(a) Insulated supply service drops limited to 300 V to ground 12.5 

(b) Insulated drip loops of supply service drops limited to 300 V to ground 10.5 

(c) Supply service drops limited to 150 V to ground and meeting Rules 230C1 or 230C3 12.0 

(d) Drip loops only of service drops limited to 150 V to ground and meeting 

Rules 230C1 or 230C3 10.0 

(e) Insulated communication service drops 1 1 .5 

8 Where the height of a building or other installation does not permit service drops to meet these values, 
the clearances may be reduced to the following: 

(feet) 

(a) Insulated supply service drops limited to 300 V to ground 10.5 

(b) Insulated drip loops of supply service drops limited to 300 V to ground 10.5 

(c) Supply service drops limited to 150 V to ground and meeting Rules 230C1 or 230C3 10.0 

(d) Drip loops only of supply service drops limited to 150 V to ground and meeting 

Rules 230C1 or 230C3 10.0 

Spaces and ways subject to pedestrians or restricted traffic only are those areas where riders on horses 

or other large animals, vehicles, or other mobile units exceeding a total height of 8 ft are prohibited by 

regulation or permanent terrain configurations, or are otherwise not normally encountered nor reasonably 

anticipated. 

Where a supply or communication line along a road is located relative to fences, ditches, embankments, 
etc., so that the ground under the line would not be expected to be traveled except by pedestrians, the clear- 
ances may be reduced to the following values: 

(feet) 

(a) Insulated communication conductor and communication cables. 9.5 

(b) Conductors of other communication circuits 9.5 

(c) Supply cables of any voltage meeting Rule 230C1 , supply cables limited to 150 V 

to ground meeting Rules 230C2 or 230C3, and neutral conductors meeting Rule 230E1 9.5 

(d) Insulated supply conductors limited to 300 V to ground 12.5 

(e) Guys 9.5 

II No clearance from ground is required for anchor guys not crossing tracks, rails, streets, driveways, 
roads, or pathways. 

This clearance may be reduced to 13 ft for communication conductors and guys. 
Where this construction crosses over or runs along alleys, driveways, or parking lots not subject to truck 
traffic this clearance may be reduced to 15 ft. 

79 
Copyright © 2001 IEEE. All rights reserved. 



I 



T-232-l(ft) PART 2. SAFETY RULES FOR OVERHEAD LINES T-232-l(ft) 

Ungrounded guys and ungrounded portions of span guys between guy insulators shall have clearances 
based on the highest voltage to which they may be exposed due to a slack conductor or guy. 

15 Anchor guys insulated in accordance with Rule 279 may have the same clearance as grounded guys. 
Adjacent to tunnels and overhead bridges that restrict the height of loaded rail cars to less than 20 ft, 
these clearances may be reduced by the difference between the highest loaded rail car 
handled and 20 ft, if mutually agreed to by the parties at interest. 

17 For controlled impoundments, the surface area and corresponding clearances shall be based upon the 
design high-water level. \ 

18 For uncontrolled water flow areas, the surface area shall be that enclosed by its annual high-water mark. 
Clearances shall be based on the normal flood level; if available, the 10-year flood level may be assumed as 
the normal flood level. 

19 The clearance over rivers, streams, and canals shall be based upon the largest surface area of any 1 -mi- 
long segment that includes the crossing. The clearance over a canal, river, or stream normally used to provide 
access for sailboats to a larger body of water shall be the same as that required for the larger body of water. 

Where an overwater obstruction restricts vessel height to less than the applicable reference height given 
in Table 232-3, the required clearance may be reduced by the difference between the reference height and the 
overwater obstruction height, except that the reduced clearance shall be not less than that required for the 
surface area on the line-crossing side of the obstruction. 
| Where the US Army Corps of Engineers, or the state, or surrogate thereof has issued a crossing permit, 

clearances of that permit shall govern. 

I See Rule 2341 for the required horizontal and diagonal clearances to rail cars. 

For the purpose of this Rule, trucks are defined as any vehicle exceeding 8 ft in height. Areas not subject 
to truck traffic are areas where truck traffic is not normally encountered nor reasonably anticipated. 

Communication cables and conductors may have a clearance of 15 ft where poles are back of curbs or 
other deterrents to vehicular traffic. 

25 The clearance values shown in this table are computed by adding the applicable Mechanical and Elec- 
trical (M & E) value of Table A-l to the applicable Reference Component of Table A-2a of Appendix A. 

I 26 When designing a line to accommodate oversized vehicles, these clearance values shall be increased by 
the difference between the known height of the oversized vehicle and 14 ft. 



80 
Copyright © 2001 IEEE. All rights reserved. 



T-232-2(m) 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-232-2(m) 



m 



Table 232-2 

Vertical Clearance of Equipment Cases, Support Arms, Platforms, Braces and 

Unguarded Rigid Live Parts Above Ground, Roadway, or Water Surfaces 8 

(Voltages are phase to ground for effectively grounded circuits and those other circuits where all ground 

faults are cleared by promptly de-energizing the faulted section, both initially and following subsequent 

breaker operations. See the definitions section for voltages of other systems. 

See Rules 232B2, 232B3, 232Cla, and 232D4.) 



Nature of surface below 


Nonmetallic 
or effectively 

grounded 

support arms 

and 

equipment 

cases 

(m) 


Unguarded rigid 
live parts of to 750 V 
and ungrounded cases 

that contain 

equipment connected 

to circuits of not more 

than 750 V 

(m) 


Unguarded rigid 

live parts of 

over 750 V to 22 kV 

and ungrounded 

cases that contain 

equipment connected 

to circuits of over 750 

V to 22 kV 

(m) 


1 . Where rigid parts overhang 








a . Roads , streets , and other areas subject to 
truck traffic 


4.6 


4.9 


5.5 


b. Driveways, parking lots, and alleys 


4.6 


4.9 ' 


5.5 


c . Other land traversed by vehicles such as 
cultivated land, grazing land, forest, 
orchard, etc. 


4.6 7 


4.9 


5.5 


d. Spaces and ways subject to pedestrians 
or restricted traffic only 


3.4 7 


s.e 1 ^ 


4.3 


2. Where rigid parts are along and within the 
limits of highways or other road rights-of- 
way but do not overhang the roadway 








a. Roads, streets, and alleys 


4.6' 


4.9 


5.5 


b. Roads in rural districts where it is 
unlikely that vehicles will be crossing 
under the line 


4.0 7 


4.3 2 


4.9 


3. Water areas not suitable for sailboating or 
where sailboating is prohibited 


4.3 


4.4 


4.6 



I 



1 This clearance may be reduced to the following values: (meters) 

(a) Insulated live parts limited to 300 V to ground 3.6 

(b) Insulated live parts limited to 150 V to ground 3.0 
Where a supply line along a road is limited to 300 V to ground and is located relative to fences, ditches, 

embankments, etc., so that the ground under the line would not be expected to be traveled except by pedes- 
trians, this clearance may be reduced to 3.6 m. 

This footnote not used in this edition. 
4 For the purpose of this rule, trucks are defined as any vehicle exceeding 2.45 m in height. Areas not sub- 
ject to truck traffic are areas where truck traffic is not normally encountered nor reasonably anticipated. 

Spaces and ways subject to pedestrians or restricted traffic only are those areas where riders on 
horseback, vehicles, or other mobile units exceeding 2.45 m in height, are prohibited by regulation or 
permanent terrain configurations or are otherwise not normally encountered nor reasonably anticipated . 

This footnote not used in this edition. 

Effectively grounded supply or communication equipment cases (such as fire alarm boxes, control boxes, 
communication terminals, meters or similar equipment cases) may be mounted at a lower level for 
accessibility, provided such cases do not unduly obstruct a walkway. 
NOTE: See also Rule 234J2c. 

The clearance values shown in this table are computed by adding the applicable Mechanical and Electri- 
cal (M & E) value of Table A-l to the applicable Reference Component of Table A-2a of Appendix A. 

Where the US Army Corps of Engineers, or the state, or surrogate thereof has issued a crossing permit, 
clearances of that permit shall govern. 



81 
Copyright © 2001 IEEE. All rights reserved. 



T-232-2(ft) 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-232-2(ft) 



ft 



Table 232-2 

Vertical Clearance of Equipment Cases, Support Arms, Platforms, Braces and 

Unguarded Rigid Live Parts Above Ground, Roadway, or Water Surfaces 8 

(Voltages are phase to ground for effectively grounded circuits and those other circuits where all ground 

faults are cleared by promptly de-energizing the faulted section, both initially and following subsequent 

breaker operations. See the definitions section for voltages of other systems. 

See Rules 232B2, 232B3, 232Cla, and 232D4.) 



Nature of surface below 


Nonmetallic or 

effectively 

grounded 

support arms 

and equipment 

cases 

(ft) 


Unguarded rigid live 
parts of to 750 V and 
ungrounded cases that 

contain equipment 

connected to circuits of 

not more than 750 V 

(ft) 


Unguarded rigid live 
parts of over 750 V to 
22 k V and ungrounded 

cases that contain 

equipment connected 

to circuits of over 750 

V to 22 kV 

(ft) 


1 . Where rigid parts overhang 








a. Roads, streets, and other areas subject 
to truck traffic 4 


15.0 


16.0 


18.0 


b. Driveways, parking lots, and alleys 


15.0 


16.0 1 


18.0 


c. Other land traversed by vehicles such 
as cultivated land, grazing land, forest, 
orchard, etc. 


15.0 7 


16.0 


18.0 


d. Spaces and ways subject to pedestrians 
or restricted traffic only 


11.0 7 


12 . io» 


14.0 


2 . Where rigid parts are along and within the 
limits of highways or other road rights- 
of-way but do not overhang the roadway 








| a. Roads, streets, and alleys 


15.0' 


16.0 


18.0 


b. Roads in rural districts where it is 
unlikely that vehicles will be crossing 
under the line 


13.0 7 


14.0 2 


16.0 


3 . Water areas not suitable for sailboating or 
where sailboating is prohibited 9 


14.0 


14.5 


15.0 



1 This clearance may be reduced to the following values: (feet) 

(a) Insulated live parts limited to 300 V to ground 12 

(b) Insulated live parts limited to 150 V to ground 10 
Where a supply line along a road is limited to 300 V to ground and is located relative to fences, ditches, 

embankments, etc., so that the ground under the line would not be expected to be traveled except by pedes- 
trians, this clearance may be reduced to 12 ft. 

3 This footnote not used in this edition. 

4 For the purpose of this rule, trucks are defined as any vehicle exceeding 8 ft in height. Areas not subject 
to truck traffic are areas where truck traffic is not normally encountered nor reasonably anticipated. 

5 Spaces and ways subject to pedestrians or restricted traffic only are those areas where riders on 
horseback, vehicles, or other mobile units exceeding 8 ft in height, are prohibited by regulation or permanent 
terrain configurations or are otherwise not normally encountered nor reasonably anticipated. 

This footnote not used in this edition. 

7 Effectively grounded supply or communication equipment cases (such as fire alarm boxes, control box- 
es, communication terminals, meters, or similar equipment cases) may be mounted at a lower level for acces- 
sibility, provided such cases do not unduly obstruct a walkway. 

NOTE: See also Rule 234J2c. 

8 The clearance values shown in this table are computed by adding the applicable Mechanical and 
Electrical (M & E) value of Table A- 1 to the applicable Reference Component of Table A-2a of Appendix A. 

9 Where the US Army Corps of Engineers, or the state, or surrogate thereof has issued a crossing permit, 
clearances of that permit shall govern. 



82 
Copyright © 2001 IEEE. All rights reserved. 



T-232-3 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-232-3 



Table 232-3 
Reference Heights 

(See Rule 232D2) 



Nature of surface underneath lines 


(m) tin 


a. Track rails of railroads (except electrified railroads using overhead trolley 
conductors) ' 


6.7 


21 


b . Streets , alleys , roads , driveways , and parking lots 


4.3 


14 


c. Spaces and ways subject to pedestrians or restricted traffic only 2 


3.0 


Id 


d. Other land, such as cultivated, grazing, forest, or orchard, that is traversed by 
vehicles 


4.3 


14 


e. Water areas not suitable for sailboating or where sailboating is prohibited 


3.8 


12.5 


f . Water areas suitable for sailboating including lakes, ponds, reservoirs, tidal waters, 
rivers, streams, and canals with unobstructed surface area ■ 






(1) Less than 0.08 km 2 (20 acres) 


4.9 


16 


(2) Over 0.08 to 0.8 km 2 (20 to 200 acres) 


7.3 


24 


(3) Over 0.8 to 8 km 2 (200 to 2000 acres) 


9.0 


30 


(4) Over 8 km 2 (2000 acres) 


11.0 


36 


g. In public or private land and water areas posted for rigging or launching sailboats, 
the reference height shall be 1 .5 m (5 ft) greater than in f above , for the type of water 
areas serviced by the launching site 







See Rule 2341 for the required horizontal and diagonal clearances to rail cars. 

Spaces and ways subject to pedestrians or restricted traffic only are those areas where riders on 
horseback, vehicles, or other mobile units exceeding 2.45 m (8 ft) in height, are prohibited by regulation or 
permanent terrain configurations or are otherwise not normally encountered nor reasonably anticipated. 

For controlled impoundments, the surface area and corresponding clearances shall be based upon the de- 
sign high- water level. For other waters, the surface area shall be that enclosed by its annual high- water mark, 
and clearances shall be based on the normal flood level. The clearances over rivers, streams, and canals shall 
be based upon the largest surface area of any 1600 m (1 mi) long segment that includes the crossing. The 
clearance over a canal or similar waterway providing access for sailboats to a larger body of water shall be 
the same as that required for the larger body of water. 

Where an overwater obstruction restricts vessel height to less than the applicable reference height, the 
required clearance may be reduced by the difference between the reference height and the overwater obstruc- 
tion height, except that the reduced clearance shall not be less than that required for the surface area on the 
line-crossing side of the obstruction. 



83 
Copyright © 2001 IEEE. All rights reserved. 



T-232-4 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-232-4 



Table 232-4 
Electrical Component of Clearance in Rule 232D3a 

(Add 3% for each 300 m (1000 ft) in excess of 450 m (1500 ft) above mean sea level. 
Increase clearance to limit electrostatic effects in accordance with Rule 232D3c.) 



Maximum 

operating voltage 

phase to phase 

(kV) 


Switching- 
surge factor 
(per unit) 


Switching 
surge 

(kV) 


Electrical 
component of clearance 


(m) 


(ft) 


242 


3.54 or less 


700 or less 


2.15 


■'■ : ';. :: ': : :7.l4'::-':',;:;: 


362 


2.37 or less 


700 or less 


2.15 


7.1' 
7~]T~ 

9.9 

10.8 : 1 : 

..;..'■'■'■ .12.7.'. -.■■■''-'■ : ' 
:;■... ; : 14.6 : : ';.;:';[ 

'■: '■, "-. 16.7: [' ''- '■ 


550 


1 .56 or less 


700 or less 


2.15 




1.90 


853 


3.0 




2.00 


898 


3.3 




2.20 


988 


3.9 




2.40 


1079 


4.4 




2.60 


1168 


5.1 


800 


1.60 


1045 


4.2 


, ;; ;. ii3.9 ■■■■;■:■ 




1.80 


1176 


5.2 


16.9 




2.00 


1306 


6.1 


20.1 

..'■■'.'■■■. 




2.10 or more 


1372 or more 


6.6 


■-;:>■', lis 2 .-.■■ ■ 



1 Limited by Rule 232D4. 

2 Limited by Rules 232A and 232B. 



84 
Copyright © 2001 IEEE. All rights reserved. 



233 PART 2. SAFETY RULES FOR OVERHEAD LINES 233A2 



233. Clearances Between Wires, Conductors, and Cables Carried on Different Supporting 
Structures 

A. General 

Crossings should be made on a common supporting structure, where practical. In other cases, the 
clearance between any two crossing or adjacent wires, conductors, or cables carried on different 
supporting structures shall be not less than that required by Rules 233B and 233C at any location in 
the spans. The clearance shall be not less than that required by application of a clearance envelope 
developed under Rule 233A2 to the positions on or within conductor movement envelopes developed 
under Rule 233A1 at which the two wires, conductors, or cables would be closest together. For 
purposes of this determination, the relevant positions of the wires, conductors, or cables on or within 
their respective conductor movement envelopes are those that can occur when (1) both are 
simultaneously subjected to the same ambient air temperature and wind loading conditions, and (2) 
each is subjected individually to the full range of its icing conditions and applicable design electrical 
loading. 

Figure 233-1 is a graphical illustration of the application of Rule 233A. Alternate methods that 
assure compliance with these rules may be used. 

1 . Conductor Movement Envelope 

a. Development 

The conductor movement envelope shall be developed from the locus of the most displaced 
conductor positions defined below and shown in Fig 233-2. 

(1) 15 °C (60 °F), no wind displacement, at both initial unloaded and final unloaded sag (con- 
ductor positions A and C). 

(2) With the wire, conductor, or cable displaced from rest by a 290 Pa (6 lb/ft 2 ) wind at both 
initial and final sag at 15 °C (60 °F). The displacement of the wire, conductor, or cable 
shall include deflection of suspension insulators and flexible structures (conductor posi- 
tions B andD). 

EXCEPTION: Where the entire span is so close to a building, terrain feature, or other obstacle as to 
be sheltered from the wind flowing across the line in either direction, the wind pressure may be re- 
duced to a 190 Pa (4 lb/ft 2 ) wind. Trees are not considered to shelter a line. 

(3) Final sag at one of the following loading conditions, whichever produces the largest sag 
(conductor position E): 

(a) 50 °C (120 °F), no wind displacement, 

(b) The maximum conductor temperature for which the line is designed to operate, if 
greater than 50 °C (120 °F), with no wind displacement, or 

(c) °C (32 °F), no wind displacement, with radial thickness of ice, if any, specified in 
Rule 250B for the loading district concerned. 

b. Sag Increase 

No sag increase for either high operating temperatures or ice loading is required for trolley and 
electrified railroad contact conductors. Rule 233Ala(3) does not apply to these conductors. 

2. Clearance Envelope 

The clearance envelope shown in Fig 233-3 shall be determined by the horizontal clearance (H) 
required by Rule 233B and the vertical clearance (V) required by Rule 233C. 



85 
Copyright © 2001 IEEE. All rights reserved. 



F-233-1 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



F-233-1 



CLOSEST WIRE, CONDUCTOR, OR 
CABLE OF CIRCUIT NO. 1 



CLEARANCE 
ENVELOPE 
DEVELOPED 
UNDER 
RULE 233A2 




CONDUCTOR MOVEMENT ENVELOPES 
DEVELOPED UNDER RULE 233AI AT THE 
LOCATION IN THE LINE WHERE WIRES, 
CONDUCTORS, OR CABLES COULD 
BE CLOSEST TOGETHER 



/ 



CLOSEST WIRE, 
CONDUCTOR, 
OR CABLE OF 
CIRCUIT NO. 2 



DIRECTION OF WIND 



RANGE OF POSSIBLE 
POSITIONS OF CONDUCTOR NO. 1 
WHEN CONDUCTOR NO. 1 
IS AT POSITION X ON 
ITS CONDUCTOR 
MOVEMENT ENVELOPE 



NOTE: In this illustration, Conductor No. 2 is closest at position X 2 to Conductor No. 1, where the latter is 
at position Xj . 

Fig 233-1 

Use of Clearance Envelope and Conductor Movement 

Envelopes to Determine Applicable Clearance 



86 
Copyright © 2001 IEEE. All rights reserved. 



F-233-2(m) 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



F-233-2(m) 



DIRECTION OF WIND 




CONDUCTOR 

MOVEMENT 

ENVELOPE 



Point 


Conductor Temperature 


Sag 


Ice Loading 


Wind 
Displacement 


A 


15 °C 5 


initial 


none 


none 


B 


15 °C 5 


initial 


none 


290Pa (note2) 


C 


15 °C 5 


final 


none 


none 


D 


15 °C 5 


final 


none 


290Pa (note2) 


E, 3 - 4 


The greater of 50 °C or 

maximum operating 

temperature 


final 


none 


none 


E 2 3 - 4 


0°C 


final 


as applicable 


none 



I 



The direction of the wind shall be that which produces the minimum distance between conductors. The 
displacement of the wires, conductors, or cables includes the deflection of suspension insulators and flexible 
structures. 

Where the entire span is so close to a building, terrain feature, or other obstacle as to be sheltered from 
the wind flowing across the line in either direction, the wind pressure may be reduced to a 190 Pa wind. Trees 
are not considered to shelter a line. 

J Point E shall be determined by whichever of the conditions described under Ej and E 2 produces the great- 
est sag. 

Line D-E shall be considered to be straight unless the actual concavity characteristics are known. 

When one conductor movement envelope is lower than that of the other conductor, the lower envelope 
shall be developed with points A, B, C, and D at a conductor temperature equal to the ambient temperature 
used in determining E of the upper conductor movement envelope. 

m 

Fig 233-2 
Conductor Movement Envelope 



87 
Copyright © 2001 IEEE. All rights reserved. 



F-233-2(ft) 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



F-233-2(ft) 



DIRECTION OF WIND 




CONDUCTOR 

MOVEMENT 

ENVELOPE 



Point 


Conductor Temperature 


Sag 


Ice Loading 


Wind Displacement 


A 


60 °F 5 


initial 


none 


none 


B 


60 °F 5 


initial 


none 


61b/ft 2(note2) 


C 


60 °F 5 


final 


none 


none 


D 


60 °F 5 


final 


none 


61b/ft 2(note2) 


E! 3 ' 4 


The greater of 120 °F 

or maximum operating 

temperature 


final 


none 


none 


E 2 3 ' 4 


32 °F 


final 


as applicable 


none 



1 The direction of the wind shall be that which produces the minimum distance between conductors. The 
displacement of the wires, conductors, or cables includes the deflection of suspension insulators and flexible 
structures. 

2 Where the entire span is so close to a building, terrain feature, or other obstacle as to be sheltered from 
the wind flowing across the line in either direction, the wind pressure may be reduced to a 4 lb/ft wind. Trees 
are not considered to shelter a line. 

3 Point E shall be determined by whichever of the conditions described under Ej and E 2 produces the 
greatest sag. 

4 Line D-E shall be considered to be straight unless the actual concavity characteristics are known. 
5 When one conductor movement envelope is lower than that of the other conductor, the lower conductor 

envelope shall be developed with points A, B , C, and D at a conductor temperature equal to the ambient tem- 
perature used in determining E of the upper conductor movement envelope. 

ft 

Fig 233-2 
Conductor Movement Envelope 



88 
Copyright © 2001 IEEE. All rights reserved. 



F-233-3 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



233C2a 



CLOSEST ALLOWABLE POSITION 
OF CONDUCTOR NO 2 




if 
H>V 



if 
H=V 



if 
H<V 



Fig 233-3 
Clearance Envelope 



B. Horizontal Clearance 

1 . Clearance Requirements 

The horizontal clearance between crossing or adjacent wires, conductors, or cables carried on dif- 
ferent supporting structures shall be not less than 1.50 m (5 ft). For voltages between the wires, 
conductors, or cables exceeding 129 kV, additional clearance of 10 mm (0.4 in) per kV over 
129 kV shall be provided. 

EXCEPTION: The horizontal clearance between anchor guys of different supporting structures may be re- 
duced to 150 mm (6 in) and may be reduced to 600 mm (2 ft) between other guys, span wires, and neutral 
conductors meeting Rule 230E1 . 

2. Alternate Clearances for Voltages Exceeding 98 kV AC to Ground or 139 kV DC to Ground 

The clearances specified in Rule 233B1 may be reduced for circuits with known switching-surge 
factors, but shall be not less than the alternate clearance derived from the computations required 
in Rules 235B3a and 235B3b. 



I 



C. Vertical Clearance 

1 . Clearance Requirements 

The vertical clearance between any crossing or adjacent wires, conductors, or cables carried on 
different supporting structures shall be not less than that shown in Table 233-1. 

EXCEPTION: No vertical clearance is required between wires, conductors, or cables that are electrically in- 
terconnected at the crossing. 

2. Voltages Exceeding 22 kV 

a. The clearance given in Table 233-1 shall be increased by the sum of the following: For the 
upper-level conductors between 22 and 470 kV, the clearance shall be increased at the rate of 
10 mm (0.4 in) per kV in excess of 22 kV. For the lower-level conductors exceeding 22 kV, 
the additional clearance shall be computed at the same rate. For voltages exceeding 470 kV, 
the clearance shall be determined by the method given in Rule 233C3. The additional clear- 
ance shall be computed using the maximum operating voltage if above 50 kV and nominal 
voltage if below 50 kV. 

89 
Copyright © 2001 IEEE. All rights reserved. 



233C2b PART 2. SAFETY RULES FOR OVERHEAD LINES 233C3c 



EXCEPTION: For voltages exceeding 98 kV ac to ground or 139 kV dc to ground, clearances less than 
those required above are permitted for systems with known switching-surge factors. (See Rule 233C3.) 

b. For voltages exceeding 50 kV, the additional clearance specified in Rule 233C2a shall be in- 
creased 3% for each 300 m (1000 ft) in excess of 1000 m (3300 ft) above mean sea level. 

Alternate Clearances for Voltage Exceeding 98 kV AC to Ground or 139 kV DC to Ground 

The clearances specified in Rules 233C1 and 233C2 may be reduced where the higher- voltage cir- 
cuit has a known switching-surge factor, but shall be not less than the alternate clearance, which 
is computed by adding the reference height from Rule 233C3a to the electrical component of 
clearance from Rule 233C3b. For these computations, communication conductors and cables, 
guys, messengers, neutral conductors meeting Rule 230E1, and supply cables meeting Rule 
230C1 shall be considered at zero voltage. 

a. Reference Heights 

The reference height shall be selected from Table 233-3. 

b. Electrical Component of Clearance 

(1) The electrical component (D) shall be computed using the following equations. Selected 
values of D are listed in Table 233-2. 



D = 1.00 



D = 3.28 



[V H ■ (PU) + V L ]a- 



500K 



1.667 



be (m) 



r[V H (PU) + V L ]a- 



500 AT 



1.667 



be (ft) 



where 



V H = higher- voltage circuit maximum ac crest operating voltage to ground or maximum 
dc operating voltage to ground in kilovolts, 

V L = lower- voltage circuit maximum ac crest operating voltage to ground or maximum 
dc operating voltage to ground in kilovolts, 

PU = higher- voltage circuit maximum switching-surge factor expressed in per-unit peak 
voltage to ground and defined as a switching-surge level for circuit breakers cor- 
responding to 98% probability that the maximum switching surge generated per 
breaker operation does not exceed this surge level, or the maximum anticipated 
switching-surge level generated by other means, whichever is greater, 

a = 1 . 1 5 , the allowance for three standard deviations , 

b = 1 .03 , the allowance for nonstandard atmospheric conditions , 

c = 1.2, the margin of safety, 

K = 1 .4, the configuration factor for conductor-to-conductor gap. 

(2) The value of D calculated by Rule 233C3b(l) shall be increased 3% for each 300 m 
(1000 ft) in excess of 450 m (1500 ft) above mean sea level. 

Limit 

The alternate clearance shall be not less than the clearance required by Rules 233C1 and 
233C2 with the lower-voltage circuit at ground potential. 

90 
Copyright © 2001 IEEE. All rights reserved. 



T-233-l(m) 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-233-l(m) 



m 
Table 233-1 
Vertical Clearance Between Wires, Conductors, 
and Cables Carried on Different Supporting Structures 

Voltages are phase to ground for effectively grounded circuits and those other circuits where all ground faults 

are cleared by promptly de-energizing the faulted section, both initially and following subsequent breaker 

operations. See the definitions section for voltages of other systems. 

See Rules 233C 1 and 233C2a.) 



Lower level 


Upper level 


Effectively 

grounded 

communication 

guys, span wires 

andmessengers, 

communication 

conductors and 

cables 

(m) 


Effectively 

grounded supply 

guys, span wires 

and messengers, 

neutral conductors 

meeting Rule 

230El,and 

surge-protection 

wires 

(m) 


Supply 

cables 

meeting Rule 

230Cl,and 

supply cables 

of to 750 V 

meeting Rule 

230C2 or 

230C3 

(m) 


Open 

supply 

conductors 

to 750 V, 

and supply 

cables over 

750 V 

meeting 

Rule230C2 

or 230C3 

(m) 


Open 

supply 

conductors 

over 750 V 

to 22 kV 

(m) 


1 . Effectively grounded 
supply guys, span wires 
and messengers, neutral 
conductors meeting 
Rule 230E1, and surge- 
protection wires 


0.60 x ' 2 


0.60 x - 2 


0.60 2 


0.60 


0.60 


2. Effectively grounded 
communication guys, 
span wires and 
messengers; 
communication 
conductors and cables 


0.60 1 ' 2 


0.60 ' 


0.60 


1.20 8 


1.50 5 


3. Supply cables meeting 
Rule 230C1, and supply 
cables of to 750 V 
meeting Rules 230C2 or 
230C3 


0.60 


0.60 


0.60 


0.60 


0.60 


4. Open supply conductors, 
to 750 V; supply cables 
over 750 V meeting 
Rule 230C2 or 230C3 


1.20 9 


0.60 


0.60 


0.60 


0.60 


5. Open supply conductors, 
750 V to 22 kV 


1.50 5 - 9 


0.60 


0.60 9 


0.60 9 


0.60 


6. Trolley and electrified 
railroad contact 
conductors and associated 
span and messenger wires 


1.20 3 


1.20 3 


1.20 3 


1.20 3 ' 4 


1.80 



I 



I No clearance is specified between guys or span wires that are electrically interconnected. 

The clearance of communication conductors and their guy, span, and messenger wires from each other 
in locations where no other classes of conductors are involved may be reduced by mutual consent of the 
| parties concerned, except for fire-alarm conductors and conductors used in the operation of railroads. 

3 Trolley and electrified railroad contact conductors of more than 750 V should have at least 1 .80 m of 
clearance. This clearance should also be provided over lower- voltage trolley and electrified railroad contact 
conductors unless the crossover conductors are beyond reach of a trolley pole leaving the trolley-contact 
conductor or are suitably protected against damage from trolley poles leaving the trolley-contact conductor. 

4 Trolley and electrified railroad feeders are exempt from this clearance requirement for contact 
conductors if they are of the same nominal voltage and of the same system. 

5 This clearance may be reduced to 1.20 m where supply conductors of 750 V to 8.7 kV cross a 
communication line more than 6 ft horizontally from a communications structure. 



91 
Copyright © 2001 IEEE. All rights reserved. 



T-233-l(m) 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-233-l(ft) 



This footnote not used in this edition. 

7 These clearances may be reduced by not more than 25% to a guy insulator, provided that full clearance 
is maintained to its metallic end fittings and the guy wires. The clearance to an insulated section of a guy 
between two insulators may be reduced by not more than 25% provided that full clearance is maintained to 
the uninsulated portion of the guy. 

8 This clearance may be reduced to 0.60 m for supply service drops. 

9 In general, this type of crossing is not recommended. 



ft 
Table 233-1 
Vertical Clearance Between Wires, Conductors, 
and Cables Carried on Different Supporting Structures 

(Voltages are phase to ground for effectively grounded circuits and those other circuits where all ground 

faults are cleared by promptly de-energizing the faulted section, both initially and following subsequent 

breaker operations. See the definitions section for voltages of other systems. 

See Rules 233C1 and 233C2a.) 



Lower level 


Upper level 


Effectively 

grounded 

communication 

guys, span 

wires and 

messengers, 

communication 

conductors and 

cables 

(ft) 


Effectively 

grounded supply 

guys, span 

wires and 

messengers, 

neutral conductors 

meeting Rule 

230E1, and 

surge-protection 

wires 

(ft) 


Supply 

cables 

meeting 

Rule 

230Cl,and 

supply 

cables of 

to 750 V 

meeting 

Rule230C2 

or 230C3 

(ft) 


Open 

supply 

conductors 

to 750 V, 

and supply 

cables over 

750 V 

meeting 

Rule230C2 

or 230C3 

(ft) 


Open 

supply 
conductor 
s over 750 
Vto22kV 

(ft) 


1 . Effectively grounded supply 
guys, span wires and 
messengers, neutral 
conductors meeting 
Rule 230E1, and surge- 
protection wires 


1,2 

2 


1,2 
2 


2 
2 


2 


2 


2 Effectively grounded 

communication guys, span 
wires and messengers; 
communication conductors 
and cables 


1,2 

2 


1 
2 


2 


8 
4 


5 

5 


3 . Supply cables meeting Rule 
230C1 , and supply cables of 
to 750 V meeting 
Rules 230C2 or 230C3 


2 


2 


2 


2 


2 


4. Open supply conductors, 
to 750 V; supply cables 
over 750 V meeting 
Rule 230C2 or 230C3 


4 9 


2 


2 


2 


2 


5. Open supply conductors, 
750 V to 22 kV 


5,9 

5 


2 


2 9 


2 9 


2 


6. Trolley and electrified 
railroad contact conductors 
and associated span and 
messenger wires 


3 

4 


3 

4 


3 

4 


3,4 
4 


6 



1 No clearance is specified between guys or span wires that are electrically interconnected. 

2 The clearance of communication conductors and their guy span, and messenger wires from each other 
in locations where no other classes of conductors are involved may be reduced by mutual consent of the par- 
ties concerned, except for fire-alarm conductors and conductors used in the operation of railroads. 



92 
Copyright © 2001 IEEE. All rights reserved. 



T-233-l(ft) PART 2. SAFETY RULES FOR OVERHEAD LINES T-233-l(ft) 



3 Trolley and electrified railroad contact conductors of more than 750 V should have at least 6 ft of 
clearance. This clearance should also be provided over lower- voltage trolley and electrified railroad contact 
conductors unless the crossover conductors are beyond reach of a trolley pole leaving the trolley-contact 
conductor or are suitably protected against damage from trolley poles leaving the trolley-contact conductor. 

4 Trolley and electrified railroad feeders are exempt from this clearance requirement for contact conduc- 
tors if they are of the same nominal voltage and of the same system. 

5 This clearance may be reduced to 4 ft where supply conductors of 750 V to 8.7 kV cross a communication 
line more than 6 ft horizontally from a communications structure. 

6 This footnote not used in this edition. 

7 These clearances may be reduced by not more than 25% to a guy insulator, provided that full clearance 
is maintained to its metallic end fittings and the guy wires. The clearance to an insulated section of a guy be- 
tween two insulators may be reduced by not more than 25% provided that full clearance is maintained to the 
uninsulated portion of the guy. 

8 This clearance may be reduced to 2 ft for supply service drops. 
In general, this type of crossing is not recommended. 



I 



93 
Copyright © 2001 IEEE. All rights reserved. 



T-233-2(m) 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-233-2(m) 



m 



Table 233-2 
Clearance Between Supply Wires, Conductors, and Cables in Rule 233C3b(l) 

(Add 3% for each 300 m in excess of 450 m above mean sea level.) 



Higher-voltage circuit 


Lower-voltage circuit 


Maximum 

operating voltage 

phase to phase 

(kV) 


Switching- 
surge factor 
(per unit) 


Maximum operating voltage phase to phase (kV) 


121 

(m) 


145 

(m) 


169 

(m) 


242 
(m) 


362 
(m) 


550 
(m) 


800 
(m) 


242 


3.3 or less 


i 
2.13 


i 
2.13 


2.13 ' 


l 
2.16 








362 


2.4 


2.80 ' 


2.80 ' 


2.80 l 


2.80 l 


2.90 








2.6 


2.80 i 


2.80 


2.80 ' 


2.80 


3.1 








2.8 


2.80 * 


2.80 ' 


2.80 l 


3.0 


3.4 








3.0 


2.80 


2.90 


3.0 


3.3 


3.7 






550 


1.8 


l 
4.0 


l 
4.0 


l 
4.0 


1 
4.0 


1 
4.0 


4.1 






2.0 


1 
4.0 


l 
4.0 


l 
4.0 


l 
4.0 


1 
4.0 


4.7 






2.2 


1 
4.0 


1 
4.0 


1 

4.0 


1 
4.0 


4.3 


5.2 






2.4 


l 
4.0 


l 

4.0 


1 
4.0 


4.3 


4.8 


5.7 






2.6 


2 

4.1 


2 

4.3 


4.4 


4.8 


5.3 


6.3 




800 


1.6 


l 
5.4 


l 
5.4 


1 
5.4 


1 

5.4 


1 
5.4 


5.6 


6.9 




1.8 


1 
5.4 


1 
5.4 


l 
5.4 


l 
5.4 


1 
5.4 


6.4 


7.7 




2.0 


l 
5.4 


l 
5.4 


1 
5.4 


5.6 


6.2 


7.0 


8.4 




2.2 


2 

5.6 


2 

5.8 


2 

5.9 


2 

6.3 


2 

7.0 


2 

8.1 


2 

9.4 



1 Limited by Rule 233C3c. 

2 Need not be greater than the values specified in Rules 233C1 and 233C2. 



94 
Copyright © 2001 IEEE. All rights reserved. 



T-233-2(ft) 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-233-3 



ft 



Table 233-2 
Clearance Between Supply Wires, Conductors, and Cables in Rule 233C3b(l) 

(Add 3% for each 1000 ft in excess of 1500 ft above mean sea level.) 



Higher-voltage circuit 


Lower-voltage circuit 


Maximum 

operating voltage 

phase to phase 

(kV) 


Switching- 
surge factor 
(per unit) 


Maximum operating voltage phase to phase (kV) 


121 

(ft) 


145 

(ft) 


169 

(ft) 


242 

(ft) 


362 

(ft) 


550 

(ft) 


800 

(ft) 


242 


3 .3 or less 


7.0 ' 


7.0 1 


7.0 ' 


l 
7.1 








362 


2.4 


9.3 1 


9.3 ' 


9.3 l 


9.3 ' 


9.4 








2.6 


9.3 ] 


9.3 ! 


9.3 i 


9.3 1 


10.3 








2.8 


9.3 ' 


9.3 ' 


9.3* 


9.7 


11.3 








3.0 


9.3 l 


9.4 1 


9.7 


10.7 


12.3 






550 


1.8 


13.0 


13.0 


13.0 ' 


13.0 l 


l 
13.0 


13.6 






2.0 


13.0 


13.0 


13.0 X 


13.0 ' 


1 
13.0 


15.3 






2.2 


13.0 


13.0 


13.0 * 


13.0 L 


14.1 


17.0 






2.4 


13.0 l 


13.0 1 


13.0 ' 


14.0 


15.8 


18.8 






2.6 


13.6 


14.1 


14.5 


15.6 


17.5 


20.7 




800 


1.6 


17.8 ' 


17.8 


17.8 ' 


1 
17.8 


1 
17.8 


18.2 


22.5 




1.8 


17.8 1 


17.8 X 


17.8 2 


l 
17.8 


17.8 


20.9 


25.4 




2.0 


17.8 l 


17.8 ' 


17.8 * 


18.4 


20.4 


23.7 


28.5 




2.2 


2 
18.4 


2 
18.9 


2 
19.4 


2 

20.8 


2 
23.1 


2 

26.7 


31.5 2 



1 Limited by Rule 233C3c. 

z Need not be greater than the values specified in Rules 233C1 and 233C2. 

Table 233-3 
Reference Heights 

(See Rule 233C3a.) 



Reference height 


(m) j (ft) 


(1) Supply lines 





(2) Communication lines 


0.60 2 



95 
Copyright © 2001 IEEE. All rights reserved. 



234 PART 2. SAFETY RULES FOR OVERHEAD LINES 234B la 



234. Clearance of Wires, Conductors, Cables, and Equipment From Buildings, Bridges, 
Rail Cars, Swimming Pools, and Other Installations 

A. Application 

1. Vertical and Horizontal Clearances (No Wind Displacement) 

The vertical and horizontal clearances specified in Rules 234B, 234C, 234D, 234E, 234F, and 
2341 apply under whichever conditions of the following conductor temperature and loading con- 
ditions produces the closest approach. Rules 234Ala, 234Alb, and 234Alc apply above and 
alongside subject installations; Rule 234Ald applies below and alongside subject installations. 

a. 50 °C (120 °F), no wind displacement, final sag. 

b. The maximum conductor temperature for which the line is designed to operate, if greater than 
50 °C (120 °F), no wind displacement, final sag. 

c. °C (32 °F), no wind displacement, final sag, with radial thickness of ice, if any, specified in 
Rule 250B for the applicable loading district. 

d. The minimum conductor temperature for which the line is designed, no wind displacement, 
initial sag. 

EXCEPTION: Vertical or lateral conductors or cables attached directly to the surface of a supporting 
structure in accordance with other rules are not subject to the provisions of this rule. 
NOTE: The phase and neutral conductors of a supply line are normally considered separately when de- 
termining the sag of each due to temperature rise. 

2. Horizontal Clearances (With Wind Displacement) 

Where consideration of horizontal displacement under wind conditions is required, the wires, con- 
ductors, or cables shall be considered to be displaced from rest toward the installation by a 290 
Pa (6 lb/ft 2 ) wind at final sag at 15 C C (60 °F). The displacement of a wire, conductor or cable 
shall include deflection of suspension insulators. The displacement of a wire, conductor, or cable 
shall also include deflection of a flexible structure if the highest wire, conductor, or cable attach- 
ment is 18 m (60 ft) or more above grade. 

EXCEPTION: Where the entire span is so close to a building, terrain feature, or other obstacle as to be shel- 
tered from the wind flowing across the line in either direction, the wind pressure may be reduced to a 190 Pa 
(4 lb/ft ) wind. Trees are not considered to shelter a line. 

3. Transition Between Horizontal and Vertical Clearances 

The horizontal clearance governs above the level of the roof or top of an installation to the point 
where the diagonal equals the vertical clearance requirement. Similarly, the horizontal clearance 
governs above or below projections from buildings, signs, or other installations to the point where 
the diagonal equals the vertical clearance requirement. From this point the transitional clearance 
shall equal the vertical clearance as shown in Figs 234- 1(a) and 234- 1(b). This rule should not be 
interpreted as restricting the installation of a trolley-contact conductor over the approximate cen- 
ter line of the track it serves. 

EXCEPTION: When the horizontal clearance is greater than the vertical clearance, the vertical clearance gov- 
erns beyond the roof or top of an installation, or projections from an installation, to the point where the diagonal 
equals the horizontal clearance requirement, as shown in Fig 234- 1(c). 

B. Clearances of Wires, Conductors, and Cables From Other Supporting Structures 

Wires, conductors, or cables of one line passing near a lighting support, traffic signal support, or a 

supporting structure of a second line, without being attached thereto, shall have clearance from any 

part of such structure not less than the following: 

1 . Horizontal Clearances 

a. A horizontal clearance, without wind, of 1.50 m (5 ft) for voltages up to 50 kV. 

EXCEPTION: For effectively grounded guys and messengers, neutrals meeting Rule 230E1, 
and cables of 300 V or less to ground meeting the requirements of Rule 230C1, 230C2, or 
230C3, the horizontal clearance may be reduced to 900 mm (3 ft). 



96 
Copyright © 2001 IEEE. All rights reserved. 



F-234-l(a) 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



F-234-l(b) 




LEGEND 

Regions Where Controlling 

Conductors Are Prohibited Clearance 



H 




Horizontal 


V 


;;S;^£S;£;;;I;:;;; 


Vertical 


T 




Transitional = 
Vertical (Arc) 



Fig 234-l(a) 
Clearance Diagram for Building 



I 





SIGN 






i : 




New sloped surface 
on bottom of the sign. 



Fig 234.1(b) 
Clearance Diagram for Other Structures 



97 
Copyright © 2001 IEEE. All rights reserved. 



F-234-l(c) 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



234B2 




BUILDING 



Fig 234-l(c) 
Transitional Clearance When H is Greater Than V 



b. When the following conductors and cables are displaced from rest under the wind conditions 
of Rule 234A2, horizontal clearances from such conductors or cables to other supporting 
structures shall be not less than those shown below: 



Conductor or cable 


Horizontal clearance required 
when displaced by wind 


(m) (ft) 


Open supply conductor, to 750 V 


1.1 ■ ; : ;■ ■ -3.5 ;' : : :■■ ; 


230C2 cable, above 750 V 


1.1 |. : ."\\'/ 3..5 /■.."■'■■ ■ 


230C3 cable, above 750 V 


i.i : . ■■■:■:; .3.5;: :: v' :, 


Open supply conductors, over 750 V to 22 kV 


1.4 [ ' : : : i: ■■ '.4.5.::'.''.' : ■■ 



See footnotes 9 and 10 to Table 234-1. 

Vertical Clearances 

A vertical clearance of 1.40 m (4.5 ft) for voltages below 22 kV and a vertical clearance of 1.70 m 

(5.5 ft) for voltages between 22 kV and 50 kV. EXCEPTIONS 1 and 2 shall not be applied 

cumulatively. 

EXCEPTION 1: For guys, messengers, and neutrals meeting Rule 230E1 and for cables of 300 V or less to 

ground meeting the requirements of Rule 230C1, 230C2, or 230C3, the vertical clearance may be reduced 

to 600 mm (2 ft). 



98 
Copyright © 2001 IEEE. All rights reserved. 



234B2 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



234C3b 



NOTE: Clearances of wires, conductors, and cables from adjacent line structure guy wires are given in 
Rule 233. 

EXCEPTION 2: The vertical clearances may be reduced by 600 mm (2 ft) if both of the following conditions 
are met: 

a. The wires, conductors, or cables above and the supporting structure of another line below are operated 
and maintained by the same utility. 

b. Employees do not work above the top of the supporting structure unless: 

(1) The upper circuit is de-energized and grounded per Rule 444D or temporarily insulated or 
repositioned, or 

(2) Other equivalent measures are taken. 

C. Clearances of Wires, Conductors, Cables, and Rigid Live Parts From Buildings, Signs, Billboards, 
Chimneys, Radio and Television Antennas, Tanks, and Other Installations Except Bridges 
1 . Vertical and Horizontal Clearances 

a. Clearances 

Unguarded or accessible wires, conductors, cables, or rigid live parts may be located adjacent 
to buildings, signs, billboards, chimneys, radio and television antennas, tanks, and other 
installations and any projections therefrom. The vertical and horizontal clearances of such 
rigid and nonrigid parts shall be not less than the values given in Table 234-1 when at rest 
under the conditions specified in Rule 234A1 . These facilities may be installed beside, over or 
under buildings, building projections and other installations, as illustrated in Figs 234- 1(a), 
234-l(b),and234-l(c). 

b. Horizontal Clearances Under Wind Displacement Conditions 

When the following conductors and cables are displaced from rest under the wind conditions 
of Rule 234A2, horizontal clearances from such conductors or cables to buildings, signs, bill- 
boards, chimneys, radio and television antennas, and other installations shall be not less than 
those shown below: 



Conductor or cable 


Horizontal clearance required when 
displaced by wind 


(m) (ft) 


Open supply conductor, to 750 V 


1.1 |.':;.-- : .--'. : .3.5.'-;- :.'- ,: '. ■' 


230C2 cable, above 750 V 


i.i '■ - : .-. /is- '.-■ /:■'■: 


230C3 cable, above 750 V 


1-1 '.-'..'. ■ : .- '-"3.5 ■■■'"',' ':.' : - 


Open supply conductors, over 750 V to 22 kV 


1.4 |: : ;■;.':.. 4,5 ■■;''..:' '■■-. 



I 



See footnotes 9 and 10 to Table 234-1. 



Guarding of Supply Conductors and Rigid Live Parts 

Where the clearances set forth in Table 234-1 cannot be obtained, supply conductors and rigid live 
parts shall be guarded. 

NOTE: Supply cables meeting Rule 230C1 are considered to be guarded within the meaning of this rule. 
Supply Conductors Attached to Buildings or Other Installations 

Where the permanent attachment of supply conductors of any class to a building or other installa- 
tion is necessary for an entrance, such conductors shall meet the following requirements over or 
along the installation to which the conductors are attached: 

a. Energized service drop conductors, including splices and taps, shall be insulated or covered in 
accordance with the following: 

(1) For to 750V, Rules 230C or 230D 

(2) For over 750 V, Rule 230C1 

This rule does not apply to neutral conductors meeting Rule 230E1. 

b. Conductors of more than 300 V to ground shall not be carried along or near the surface of the 
installation unless they are guarded or made inaccessible. 

99 

Copyright © 2001 IEEE. All rights reserved. 



234C3c PART 2 . SAFETY RULES FOR OVERHEAD LINES 234C5 



Ic. Wires or cables attached to and run along side the installation shall have clearances from the 
surface of the installation not less than 75 mm (3 in), 
d. Service-drop conductors, including drip loops, shall not be readily accessible, and they shall 
have a clearance of not less than the following: 

| (1) 2.45 m (8 ft) vertical clearance from the highest point of roofs or balconies over which 

they pass. 

EXCEPTION I: Where the voltage between conductors meeting Rule 230D does not exceed 
300 V, or where the voltage of cables meeting Rule 230C2 or 230C3 does not exceed 750 V, or 
where the cable meets Rule 230C1, and the roof or balcony is not readily accessible, the clearance 
may be not less than 900 mm (3 ft). A roof or a balcony is considered readily accessible to pedes- 
trians if it can be casually accessed through a doorway, window, ramp, stairway, or permanently 
mounted ladder by a person, on foot, who neither exerts extraordinary physical effort nor employs 
special tools or devices to gain entry. A permanently mounted ladder is not considered a means of 
access if its bottom rung is 2.45 m (8 ft) or more from the ground or other permanently installed 
accessible surface. 

EXCEPTION 2: Where a roof or a balcony is not readily accessible, and a service drop meeting 
one of the following conditions passes over a roof to terminate at a (through-the-roof) raceway or 
approved support located not more than 1 .20 m (4 ft), measured horizontally from the nearest edge 
of the roof, the clearance above the roof may be maintained at not less than 457 mm (18 in) for a 
horizontal distance of 1.8 m (6 ft) from the raceway or support, and may be maintained at not less 
than 900 mm (3 ft) for the remainder of the horizontal distance that the cable or conductor passes 
over the roof. 

| (a) Voltage between conductors meeting Rule 230D of 300 V or less, 

(b) Cables of 750 V or less meeting Rules 230C2 or 230C3, or 

| (c) Cables meeting Rule 230C 1 . 

NOTE: See Fig 234-2. 
(2) 900 mm (3 ft) in any direction from windows, doors, porches, fire escapes, or similar 
locations. 

EXCEPTION 1: This does not apply to service-drop conductors meeting Rule 230C3 above the top 
level of a window. 
EXCEPTION 2: This does not apply to windows that are not designed to open. 

4. Communication Conductors Attached to Buildings or Other Installations 
Communication conductors and cables may be attached directly to buildings or other 
installations. 

5. Ladder Space 

Where buildings or other installations exceed three stories [or 15 m (50 ft)] in height, overhead 
lines should be arranged where practical so that a clear space or zone at least 1.8 m (6 ft) wide 
will be left either adjacent to the building or beginning not over 2.45 m (8 ft) from the building 
to facilitate the raising of ladders where necessary for fire fighting. 

EXCEPTION: This requirement does not apply where it is the unvarying rule of the local fire departments 
to exclude the use of ladders in alleys or other restricted places that are generally occupied by supply con- 
ductors and cables. 



100 
Copyright ©2001 IEEE. All rights reserved. 



T-234-l(m) 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-234-l(m) 



m 

Table 234-1 
Clearance of Wires, Conductors, Cables, and Unguarded Rigid Live Parts 
Adjacent but Not Attached to Buildings and Other Installations Except Bridges 

(Voltages are phase to ground for effectively grounded circuits and those other circuits where all ground faults 

are cleared by promptly de-energizing the faulted section, both initially and following subsequent breaker 

operations. See the definitions section for voltages of other systems. Clearances are with no wind 

displacement except where stated in the footnotes below. 

See Rules 234Cla, 234C2, and 234H4.) 



Clearance of 


Insulated 

communication 

conductors and 

cables; 

messengers; 

surge-protection 

wires; grounded 

guys; 

ungrounded 

guys exposed to 

to 300 V 13 ; 

neutral 

conductors 

meeting Rule 

230E1; supply 

cables meeting 

Rule 230CF 

(m) 


Supply 

cables of 

to 750 V 

meeting 

Rules 
230C2 or 

230C3 
(m) 


Unguarded 

rigid live parts, 

to 750 V; 

noninsulated 

communication 

conductors; 

ungrounded 

equipment 

cases, to 

750 V; and 

ungrounded 

guys exposed to 

open supply 

conductors of 

over 300 V to 

750 V 5 

(m) 


Supply 

cables over 

750 V 

meeting 

Rules 

230C2 or 

230C3; 

open supply 

conductors, 

to 750 V 

(m) 


Unguarded 

rigid live 

parts, over 

750 V to 

22 kV; 

ungrounded 

equipment 

cases, 

750 V to 

22 kV; 

ungrounded 

guys 

exposed to 

over 750V 

to 22 kV 5 

(m) 


Open supply 

conductors, 

over 750 V 

to 22 kV 

(m) 


1. Buildings 














a. Horizontal 














(1) To walls, 
projections, and 
guarded windows 


1.40 1 - 2 ' 7 


1.50 1 ' 2 


1.50 1,2 


1.70 1 ' 2 ' 9 


2.00 1 ' 2 


2.301.2.10.H 


(2) To unguarded 
windows 8 


1.40 


1.50 


1.50 


1.70 9 


2.00 


2.30 10 ' u 


(3) To balconies 
and areas readily 
accessible to 
pedestrians 


1.40 


1.50 


1.50 


1.70 9 


2.00 


2.30 10 - n 


b. Vertical 14 














(1) Over or under 
roofs or projections 
not readily accessible 
to pedestrians 3 


0.90 


1.07 


3.0 


3.2 


3.6 


3.8 


(2) Over or under 
balconies and roofs 
readily accessible to 
pedestrians 3 


3.2 


3.4 


3.4 


3.5 


4.0 


4.1 


(3) Over roofs 
accessible to vehicles 
but not subject to truck 
traffic 6 


3.2 


3.4 


3.4 


3.5 


4.0 


4.1 


(4) Over roofs 
accessible to truck 
traffic 6 


4.7 


4.9 


4.9 


5.0 


5.5 


5.6 



I 



101 
Copyright © 2001 IEEE. All rights reserved. 



T-234-l(m) 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-234-l(m) 



12 



m 

Table 234-1 (Continued) 
Clearance of Wires, Conductors, Cables, and Unguarded Rigid Live Parts 
Adjacent but Not Attached to Buildings and Other Installations Except Bridges 

(Voltages are phase to ground for effectively grounded circuits and those other circuits where all ground faults 

are cleared by promptly de-energizing the faulted section, both initially and following subsequent breaker 

operations. See the definitions section for voltages of other systems. Clearances are with no wind 

displacement except where stated in the footnotes below. 

See Rules 234Cla, 234C2, and 234H4.) 



Clearance of 


Insulated 

communication 

conductors and 

cables; 

messengers; 

surge-protection 

wires; grounded 

guys; 

ungrounded 

guys exposed to 

to 300 V 13 ; 

neutral 

conductors 

meeting Rule 

230E1; supply 

cables meeting 

Rule 230C1^ 

(m) 


Supply 

cables of 

to 750 V 

meeting 

Rules 

230C2 or 

230C3 

(m) 


Unguarded 

rigid live parts, 

to 750 V; 

noninsulated 

communication 

conductors; 

ungrounded 

equipment 

cases, to 

750 V; and 

ungrounded 

guys exposed to 

open supply 

conductors of 

over 300 V to 

750 V 5 

(m) 


Supply 

cables over 

750 V 

meeting 

Rules 

230C2 or 

230C3; 

open supply 

conductors, 

to 750 V 

(m) 


Unguarded 

rigid live 

parts, over 

750 V to 

22 kV; 

ungrounded 

equipment 

cases, 

750 V to 

22 kV; 

ungrounded 

guys 

exposed to 

over 750V 

to 22 kV 5 

(m) 


Open supply 
conductors, 

over 750 V 

to 22 kV 

(m) 


2. Signs, chimneys, 
billboards, radio and 
television antennas, 
tanks, and other 
installations not 
classified as buildings 
or bridges 














a. Horizontal 4 














(1) To portions 
that are readily 
accessible to 
pedestrians 


1.40 


1.50 


1.50 


1.70 9 


2.00 


230 io,n 


(2) To portions 
that are not readily 
accessible to 
pedestrians 


0.90 


1.07 


1.50 1 ' 2 


1.70 1 - 2 - 9 


2.00 1 - 2 


2 30 1,2, 10, 11 


b. Vertical 














(1) Over or under 
catwalks and other 
surfaces upon which 
personnel walk 


3.2 


3.4 


3.4 


3.5 


4.0 


4.1 


(2) Over or under 
other portions of such 
installations 4 


0.90 


1.07 


1.70 


1.80 1 


2.45 


2.30 



102 
Copyright ©2001 IEEE. All rights reserved. 



T-234-l(m) part 2. SAFETY RULES FOR OVERHEAD LINES T-234-l(m) 



1 Where building, sign, chimney, antenna, tank, or other installation does not require maintenance such as 
painting, washing, changing of sign letters, or other operations that would require persons to work or pass 
between wires, conductors, cables, or unguarded rigid live parts and structure, the clearance may be reduced 
by 0.60 m. 

2 Where available space will not permit this value, the clearance may be reduced by 0.60 m wires, provided 
the wires, conductors, or cables, including splices and taps, and unguarded rigid live parts have a covering 
that provides sufficient dielectric strength to limit the likelihood of a short circuit in case of momentary 
contact with a structure or building. 

A roof, balcony, or area is considered readily accessible to pedestrians if it can be casually accessed 
through a doorway, ramp, window, stairway, or permanently mounted ladder by a person on foot who neither 
exerts extraordinary physical effort nor employs special tools or devices to gain entry. A permanently mount- 
ed ladder is not considered a means of access if its bottom rung is 2.45 m or more from the ground or other 
permanently installed accessible surface. 

4 The required clearances shall be to the closest approach of motorized signs or moving portions of instal- 
lations covered by Rule 234C. 

Ungrounded guys and ungrounded portions of guys between guy insulators shall have clearances based 
on the highest voltage to which they may be exposed to a slack conductor or guy. 

For the purpose of this rule, trucks are defined as any vehicle exceeding 2.45 m in height. 

This clearance may be reduced to 75 mm for the grounded portions of guys. 

Windows not designed to open may have the clearances permitted for walls and projections. 

The clearance at rest shall be not less than the value shown in this table. Also, when the conductor or 
I cable is displaced by wind, the clearance shall be not less than 1.07 m; see Rule 234Clb. 

The clearance at rest shall be not less than the value shown in this table. Also, when the conductor or 
cable is displaced by wind, the clearance shall be not less than 1.40 m; see Rule 234Clb. 

11 Where available space will not permit this value, the clearance may be reduced to 2.00 m for conductors 
limited to 8.7 kV to ground. 

12 The clearance values shown in this table are computed by adding the applicable Mechanical and Elec- 
trical (M & E) value of Table A-l to the applicable Reference Component of Table A-2b of Appendix A. 

The anchor end of guys insulated in accordance with Rule 279 may have the same clearance as grounded 
guys. 

For clearances above railings, walls, or parapets around balconies or roofs, use the clearances required 
for row lb(l). For such clearances where an outside stairway exists, use the clearances required for row 
2b(2). 



I 



103 
Copyright © 2001 IEEE. All rights reserved. 



T-234-l(ft) 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-234-l(ft) 



ft 
Table 234-1 
Clearance of Wires, Conductors, Cables, and Unguarded Rigid Live Parts 
Adjacent but Not Attached to Buildings and Other Installations Except Bridges 12 

(Voltages are phase to ground for effectively grounded circuits and those other circuits where all ground faults 

are cleared by promptly de-energizing the faulted section, both initially and following subsequent breaker 

operations. See the definitions section for voltages of other systems. Clearances are with no wind 

displacement except where stated in the footnotes below. 

See Rules 234Cla, 234C2, and 234H4.) 



Clearance of 


Insulated 

communication 

conductors and 

cables; 

messengers; 

surge- 
protection 
wires; 
grounded guys; 

ungrounded 

guys exposed to 

to 300 V 13 ; 

neutral 

conductors 

meeting Rule 

230E1; supply 

cables meeting 

Rule 230C1 5 

(ft) 


Supply 

cables of 

Oto 

750 V 

meeting 

Rules 

230C2 

or 

230C3 

(ft) 


Unguarded 
rigid live parts, 

to 750 V; 

non-insulated 

communication 

conductors; 

ungrounded 

equipment 

cases, to 

750 V; 

ungrounded 

guys exposed to 

open supply 

conductors of 

over 300 V to 

750 V 5 

(ft) 


Supply 

cables over 

750 V 

meeting 

Rules 

230C2 or 

230C3; 

open 

supply 

conductors, 

to 750 V 

(ft) 


Unguarded 

rigid live 

parts, over 

750 V to 

22 kV; 

ungrounded 

equipment 

cases, 750 V 

to 22 kV; 
ungrounded 

guys 

exposed to 

over 750V 

to 22 kV 5 

(ft) 


Open 

supply 

conductors, 

over 750 V 

to 22 kV 

(ft) 


1. Buildings 














a. Horizontal 














(1) To walls, 
projections, and guarded 
windows 


4.51,2.7 


5.0 1 ' 2 


5.0 1 - 2 


1,2,9 
5.5 


7.0 1 - 2 


1,2, 10, 11 
7.5 


(2) To unguarded 
windows 


4.5 


5.0 


5.0 


5.5 9 


7.0 


7.5 10 - 11 


(3) To balconies and 
areas readily accessible to 
pedestrians 


4.5 


5.0 


5.0 


9 
5.5 


7.0 


10,11 
7.5 


b. Vertical 14 














(1) Over or under 
roofs or projections not 
readily accessible to 
pedestrians 


3.0 


3.5 


10.0 


10.5 


12.0 


12.5 


(2) Over or under 
balconies and roofs readily 
accessible to pedestrians 


10.5 


11.0 


11.0 


11.5 


13.0 


13.5 


(3) Over roofs 
accessible to vehicles but 
not subject to truck traffic 6 


10.5 


11.0 


11.0 


11.5 


13.0 


13.5 


(4) Over roofs 

6 
accessible to truck traffic 


15.5 


16.0 


16.0 


16.5 


18.0 


18.5 



104 
Copyright © 2001 IEEE. All rights reserved. 



T-234-l(ft) 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-234-l(ft) 



ft 
Table 234-1 (Continued) 
Clearance of Wires, Conductors, Cables, and Unguarded Rigid Live Parts 
Adjacent but Not Attached to Buildings and Other Installations Except Bridges 12 

(Voltages are phase to ground for effectively grounded circuits and those other circuits where all ground faults 

are cleared by promptly de-energizing the faulted section, both initially and following subsequent breaker 

operations. See the definitions section for voltages of other systems. Clearances are with no wind 

displacement except where stated in the footnotes below. 

See Rules 234Cla, 234C2, and 234H4.) 



Clearance of 


Insulated 

communication 

conductors and 

cables; 

messengers; 

surge- 
protection 
wires; 
grounded guys; 

ungrounded 

guys exposed to 

to 300 V 13 ; 

neutral 

conductors 

meeting Rule 

230E1; supply 

cables meeting 

Rule 230C1 5 

(ft) 


Supply 

cables of 

Oto 

750 V 

meeting 

Rules 

230C2 

or 

230C3 

(ft) 


Unguarded 
rigid live parts, 

to 750 V; 

non-insulated 

communication 

conductors; 

ungrounded 

equipment 

cases, to 

750 V; 

ungrounded 

guys exposed to 

open supply 

conductors of 

over 300 V to 

750 V s 

(ft) 


Supply 

cables over 

750 V 

meeting 

Rules 

230C2 or 

230C3; 

open 

supply 

conductors, 

to 750 V 

(ft) 


Unguarded 

rigid live 

parts, over 

750 V to 

22 kV; 

ungrounded 

equipment 

cases, 750 V 

to 22 kV; 
ungrounded 

guys 

exposed to 

over 750V 

to 22 kV 5 

(ft) 


Open 

supply 

conductors, 

over 750 V 

to 22 kV 

(ft) 


2. Signs, chimneys, 
billboards, radio and 
television antennas, 
tanks, and other 
installations not classified 
as buildings or bridges 














a. Horizontal 4 














(1) To portions that 
are readily accessible to 
pedestrians 


4.5 


5.0 


5.0 1 ' 2 


5.5 9 


7.0 1 - 2 


7.5 10 - 11 


(2) To portions that 
are not readily accessible to 
pedestrians 


3.0 


3.5 


5.0 1 - 2 


5.5 1 ' 2 - 9 


7.0 1 - 2 


7 5 1,2. 10, 11 


b. Vertical 














(1) Over or under 
catwalks and other 
surfaces upon which 
personnel walk 


10.5 


11.0 


11.0 


11.5 


13.0 


13.5 


(2) Over or under 
other portions of such 
installations 


3.0 


3.5 


5.5 


6.0 1 


7.5 


8.0 






105 
Copyright © 2001 IEEE. All rights reserved. 



T-234-l(ft) PART 2. SAFETY RULES FOR OVERHEAD LINES T-234-l(ft) 



1 Where building, sign, chimney, antenna, tank, or other installation does not require maintenance such 
as painting, washing, changing of sign letters, or other operations that would require persons to work or pass 
between wires, conductors, cables or unguarded rigid live parts and structure, the clearance may be reduced 
by 2 ft. 

2 Where available space will not permit this value, the clearance may be reduced by 2 ft provided the 
wires, conductors, or cables, including splices and taps, and unguarded rigid live parts have a covering that 
provides sufficient dielectric strength to limit the likelihood of a short circuit in case of momentary contact 
with a structure or building. 

3 A roof, balcony, or area is considered readily accessible to pedestrians if it can be casually accessed 
through a doorway, ramp, window, stairway, or permanently mounted ladder by a person on foot who neither 
exerts extraordinary physical effort nor employs special tools or devices to gain entry. A permanently 
mounted ladder is not considered a means of access if its bottom rung is 8 ft or more from the ground or other 
permanently installed accessible surface. 

4 The required clearances shall be to the closest approach of motorized signs or moving portions of instal- 
lations covered by Rule 234C. 

5 Ungrounded guys and ungrounded portion of guys between guy insulators shall have clearances based 
on the highest voltage to which they may be exposed to a slack conductor or guy. 

" For the purpose of this rule, trucks are defined as any vehicle exceeding 8 ft in height. 

' This clearance may be reduced to 3 in for the grounded portions of guys. 

° Windows not designed to open may have the clearances permitted for walls and projections. 

" The clearance at rest shall be not less than the value shown in this table. Also, when the conductor or 
cable is displaced by wind, the clearance shall be not less than 3.5 ft; see Rule 234Clb. 

1" The clearance at rest shall be not less than the value shown in this table. Also, when the conductor or 
cable is displaced by wind, the clearance shall be not less than 4.5 ft; see Rule 234Clb. 

1 * Where available space will not permit this value, the clearance may be reduced to 7.0 ft for conductors 
limited to 8.7 kV to ground. 

12 The clearance values shown in this table are computed by adding the applicable Mechanical and Elec- 
trical (M & E) value of Table A-l to the applicable Reference Component of Table A-2b of Appendix A. 

The anchor end of guys insulated in accordance with Rule 279 may have the same clearance as grounded 
guys. 

14 For clearances above railings, walls, or parapets around balconies or roofs, use the clearances required 
for row lb(l). For such clearances where an outside stairway exists, use the clearances required for row 
2b(2). 



106 
Copyright © 2001 IEEE. All rights reserved. 



234D 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



234Dlb 



D. Clearance of Wires, Conductors, Cables, and Unguarded Rigid Live Parts From Bridges 
1 . Vertical and Horizontal Clearances 

a. Clearances 

Unguarded or accessible wires, conductors, cables, or rigid live parts may be located adjacent 
to or within a bridge structure. The vertical and horizontal clearances of such rigid and non- 
rigid parts shall be not less than the values given in Table 234-2 when at rest under the condi- 
tions specified in Rule 234A1, as illustrated in Figs 234- 1(a) and 234- 1(b). 
EXCEPTION: This rule does not apply to insulated communication cables, effectively grounded guys, 
span wires, and surge protection wires; neutrals meeting Rule 230E1; and supply cables meeting Rule 
230C1. 

b. Horizontal Clearances Under Wind Displacement Conditions 

When the following conductors and cables are displaced from rest under the wind conditions 
of Rule 234A2, horizontal clearances from such conductors or cables to bridges shall be not 
less than those shown below: 



Conductor or cable 


Horizontal clearance required when 
displaced by wind 


(m) .■■: ,' : : \: .(ft) . \ . 


Open supply conductor, to 750 V 


1.1 ". .: : . : : .3.5. ;■'.■.::; ; 


230C2 cable, above 750 V 


1.1 \ 3.5 


230C3 cable, above 750 V 


1.1 3.5 


Open supply conductors, over 750 V to 22 kV 


1-4 4.5 



See footnotes 8 and 9 to Table 234-2. 



107 
Copyright © 2001 IEEE. All rights reserved. 



F-234-2 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



F-234-2 



Maintain not less than 0.90m 
(3'-0") vertical clearance 
above roof outside of 1 .80m 
(6-0") radius from the 
service mast. 



Maintain not less than 
450mm (18") vertical 
clearance above roof within 
1 .80m (6'-0") radius from 
the service mast. 



1.3m ft? 0"}: 



1.20m (4 ft) max .' 



Plan View 



1.8m(6'-0") i 




Elevation View 

Fig 234-2 
Clearances of Service Drop Terminating on Support Mast 



108 
Copyright © 2001 IEEE. All rights reserved. 



234D2 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



F-234-3 



2. Guarding Trolley-Contact Conductors Located Under Bridges 

a. Where Guarding Is Required 

Guarding is required where the trolley-contact conductor is located so that a trolley pole leav- 
ing the conductor can make simultaneous contact between it and the bridge structure. 

b. Nature of Guarding 

Guarding shall consist of a substantial inverted trough of nonconducting material located 
above the contact conductor, or of other suitable means of limiting the likelihood of contact 
between the trolley support and the bridge structure. 

E. Clearance of Wires, Conductors, Cables, or Unguarded Rigid Live Parts Installed Over or Near 
Swimming Areas With No Wind Displacement 

1. Swimming Pools 

Where wires, conductors, cables, or unguarded rigid live parts are over a swimming pool or the 
surrounding area, the clearances in any direction shall be not less than those shown in Table 234- 
3 and illustrated in Fig 234-3. 

EXCEPTION 1: This rule does not apply to a pool fully enclosed by a solid or screened permanent structure. 
EXCEPTION 2: This rule does not apply to communication conductors and cables, effectively grounded 
surge-protection wires, neutral conductors meeting Rule 230E1, guys and messengers, supply cables meet- 
ing Rule 230C1, and supply cables of to 750 V meeting Rules 230C2 or 230C3 when these facilities are 
3 m (10 ft) or more horizontally from the edge of the pool, diving platform, or diving tower. 

2. Beaches and Waterways Restricted to Swimming 

Where rescue poles are used by lifeguards at supervised swimming beaches, the vertical and hor- 
izontal clearances shall be not less than those shown in Table 234-3. Where rescue poles are not 
used, the clearances shall be as specified in Rule 232. 

3. Waterways Subject to Water Skiing 

The vertical clearance shall be the same as that specified in Rule 232. 




I 



Fig 234-3 
Swimming Pool Clearances 



109 
Copyright © 2001 IEEE. All rights reserved. 



T-234-2(m) 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-234-2(m) 



m 

Table 234-2 

Clearance of Wires, Conductors, Cables, 

and Unguarded Rigid Live Parts From Bridges 

(Voltages are phase to ground for effectively grounded circuits and those other circuits where all ground 

faults are cleared by promptly de-energizing the faulted section, both initially and following subsequent 

breaker operations. See the definitions section for voltages of other systems. Clearances are with no wind 

displacement except where stated in the footnotes below. 

See Rules 234D 1 a and 234H4.) 





Unguarded rigid 
live parts, to 

750 V; 

noninsulated 

communication 

conductors,* supply 

cables of to 750 V 

meeting Rules 
230C2 or 230C3 7 ,- 

ungrounded 
equipment cases, 

to 750 V; 

ungrounded guys 

exposed to open 

supply conductors 

over 300 V to 750 

V 4 

(m) 


Supply cables over 

750 V meeting 

Rules 230C2 or 

230C3 7 ; open 

supply conductors, 

to 750 V 

(m) 


Open 

supply 

conductors, 

over 750 V 

to 22 kV 

(m) 


Unguarded 

rigid live 

parts, over 

750 V to 

22 kV, 

ungrounded 

equipment 

cases, 750 V to 

22 kV; 

ungrounded 

guys exposed 

to open 

supply 

conductors of 

over 750 V to 

22 kV 4 

(m) 


1. Clearance over bridges 










a. Attached 3 


0.90 


1.07 


1.70 


1.50 


b. Not attached 


3.0 


3.2 


3.8 


3.6 


2. Clearance beside, under, or within 
bridge structure 6 










a. Readily accessible portions of 
any bridge including wing, 
walls, and bridge attachments l 










(1) Attached 3 


0.90 


1.07 8 


1.70 9 


1.50 


(2) Not attached 


1.50 


1.70 8 


2.30 9 


2.00 


b. Ordinarily inaccessible 

portions of bridges (other than 
brick, concrete, or masonry) 
and from abutments 










(1) Attached 3 ' 5 


0.90 


1.07 8 


1.70 9 


1.50 


(2) Not attached 4 ' 5 


1.20 


1.40 8 


2.00 9 


1.80 



I 



1 Where over traveled ways on or near bridges, the clearances of Rule 232 apply also. 

2 Bridge seats of steel bridges carried on masonry, brick, or concrete abutments that require frequent 
access for inspection shall be considered as readily accessible portions. 

3 Clearance from supply conductors to supporting arms and brackets attached to bridges shall be the same 
as specified in Table 235-6 (Rule 235E1) if the supporting arms and brackets are owned, operated, or 
maintained by the same utility. 

Ungrounded guys and ungrounded portions of guys between guy insulators shall have clearances based 
on the highest voltage to which they may be exposed due to a slack conductor or guy. 

^ Where conductors passing under bridges are adequately guarded against contact by unauthorized 
| persons and can be deenergized and grounded per Rule 444D for maintenance of the bridge, clearances of the 
conductors from the bridge, at any point, may have the clearances specified in Table 235-6 for clearance from 
surfaces of support arms plus one-half the final unloaded sag of the conductor at that point. 



110 
Copyright © 2001 IEEE. All rights reserved. 



T-234-2(m) 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-234-2(ft) 



" Where the bridge has moving parts, such as a lift bridge, the required clearances shall be maintained 
throughout the full range of movement of the bridge or any attachment thereto. 

' Where permitted by the bridge owner, supply cables may be run in rigid conduit attached directly to the 
bridge. Refer to Part 3 for installation rules. 

° The clearance at rest shall be not less than the value shown in this table. Also, when the conductor or cable 
| is displaced by wind, the clearance shall be not less than 1.07 m; see Rule 234Dlb. 

y The clearance at rest shall be not less than the value shown in this table. Also, when the conductor or cable 
is displaced by wind, the clearance shall be not less than 1.40 m; see Rule 234Dlb. 

ft 

Table 234-2 

Clearance of Wires, Conductors, Cables, 

and Unguarded Rigid Live Parts From Bridges 

(Voltages are phase to ground for effectively grounded circuits and those other circuits where all ground faults 
are cleared by promptly de-energizing the faulted section, both initially and following subsequent breaker op- 
erations. See the definitions section for voltages of other systems. Clearances are with no wind displacement 

except where stated in the footnotes below. 
See Rules 234Dla and 234H4.) 







Unguarded rigid live 












parts, to 750 V; 






Unguarded rigid 






noninsulated 






live parts, over 






communication 


Supply cables 




750 V to 22 kV, 






conductors; supply 


over 750 V 




ungrounded 






cables of to 750 V 


meeting Rules 


Open supply 


equipment cases, 






meeting Rules 230C2 


230C2 or 


conductors, 


750 V to 22 kV; 


1 




or 230C3 7 , 


230C3 7 ; open 


over 750 V to 


ungrounded 






ungrounded 


supply 


22 kV 


guys exposed to 






equipment cases, to 


conductors, to 


(ft) 


open supply 






750 V; ungrounded 


750 V 




conductors of 






guys exposed to open 


(ft) 




over 750V to 






supply conductors 






22 kV 4 






over 300 V to 750 V 4 






(ft) 






(ft) 










1. Clearance over bridges 


3.0 


3.5 


5.5 


5.0 




a. Attached 3 












b. Not attached 


10.0 


10.5 . 


12.5 


12.0 




2. Clearance beside, under, or 
within bridge structure 






















a. Readily accessible portions 












of any bridge including wing, 












walls, and bridge 












attachments ' 










1 


(1) Attached 3 


3.0 


3.5 8 


5.5 9 


5.0 




(2) Not attached 


5.0 


5.5 8 


7.5 9 


7.0 




b. Ordinarily inaccessible 












portions of bridges (other 












than brick, concrete, or 












masonry) and from 












abutments 2 










1 


(1) Attached 3 ' 5 


3.0 


3.5 8 


5.5 9 


5.0 




(2) Not attached 4 > 5 


4.0 


4.5 8 


6.5 9 


6.0 



1 Where over traveled ways on or near bridges, the clearances of Rule 232 apply also. 

2 Bridge seats of steel bridges carried on masonry, brick, or concrete abutments that require frequent access 
for inspection shall be considered as readily accessible portions. 

3 Clearance from supply conductors to supporting arms and brackets attached to bridges shall be the same 
as specified in Table 235-6 (Rule 235E1) if the supporting arms and brackets are owned, operated, or main- 
tained by the same utility. 



Ill 
Copyright ©2001 IEEE. All rights reserved. 



T-234-2(ft) PART 2. SAFETY RULES FOR OVERHEAD LINES T-234-2(ft) 



^ Ungrounded guys and ungrounded portions of guys between guy insulators shall have clearances based 
on the highest voltage to which they may be exposed due to a slack conductor or guy. 

* Where conductors passing under bridges are adequately guarded against contact by unauthorized per- 
sons and can be de-energized and grounded per Rule 444D for maintenance of the bridge, clearances of the 
conductors from the bridge, at any point, may have the clearances specified in Table 235-6 for clearance from 
surfaces of support arms plus one-half the final unloaded sag of the conductor at that point. 

6 Where the bridge has moving parts, such as a lift bridge, the required clearances shall be maintained 
throughout the full range of movement of the bridge or any attachment thereto. 

' Where permitted by the bridge owner, supply cables may be run in rigid conduit attached directly to the 
bridge. Refer to Part 3 for installation rules. 

° The clearance at rest shall be not less than the value shown in this table. Also, when the conductor or 
cable is displaced by wind, the clearance shall be not less than 3.5 ft; see Rule 234Dlb. 

" The clearance at rest shall be not less than the value shown in this table. Also, when the conductor or 
cable is displaced by wind, the clearance shall be not less than 4.5 ft; see Rule 234Dlb. 



112 
Copyright © 2001 IEEE. All rights reserved. 



T-234-3(m) 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-234-3(m) 



m 



Table 234-3 
Clearance of Wires, Conductors, Cables, or Unguarded Rigid Live Parts Over or 

Near Swimming Pools * 

(Voltages are phase to ground for effectively grounded circuits and those other circuits where all ground 

faults are cleared by promptly de-energizing the faulted section, both initially and following subsequent 

breaker operations. See the definitions section for voltages of other systems. 

Clearances are with no wind displacement. 

See Rules 234E1, 234E2, and 234H4.) 





Insulated 


Unguarded rigid 










communication 


live parts, to 










conductors and 


750 V; 










cables; 


noninsulated 




Unguarded 






messengers; 


communication 


Supply cables 


rigid live 






surge-protection 


conductors; 


over 750 V 


parts over 






wires; grounded 


supply cables of 


meeting Rules 


750 V to 


Open supply 




guys; 


to 750 V 


230C2 or 


22 kV; 


conductors, 




ungrounded guys 


meeting Rules 


230C3; open 


ungrounded 


over 750 V 




exposed to to 


230C2or230C3; 


supply 


guys 


to 22 kV 




300 V 3 ; neutral 


ungrounded 


conductors, to 


exposed to 


(m) 




conductors 


guys exposed to 


750 V 


over 750 V 
to22kV 2 






meeting Rule 


open supply 


(m) 






230E1; supply 


conductors of 




(m) 






cables meeting 


over 300 V to 










Rule 230C1 


750 V 2 










(m) 


(m) 








A. Clearance in any 












direction from the 












water level, edge of 












pool, base of diving 












platform, or 












anchored raft 


6.7 


6.9 


7.0 


7.5 


7.6 


B. Clearance in any 












direction to the 












diving platform or 












tower 


4.3 


4.4 


4.6 


5.1 


5.2 


V. Vertical clearance 












over adjacent land 




Clearance shall t 


>e as required by Rule 232. 





NOTE: A, B, and V are shown in Fig 234-3. 

1 The clearance values shown in this table are computed by adding the applicable Mechanical and Electri- 
cal (M & E) value of Table A-l to the applicable Reference Component of Table A-2b of Appendix A. 

2 Ungrounded guys and ungrounded portions of guys between guy insulators shall have clearances based 
on the highest voltage to which they may be exposed due to a slack conductor or guy. 

■2 

Anchor guys insulated in accordance with Rule 279 may have the same clearance as grounded guys. 



113 
Copyright © 2001 IEEE. All rights reserved. 



T-234-3(ft) 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-234-3(ft) 



ft 



Table 234-3 
Clearance of Wires, Conductors, Cables, or Unguarded Rigid Live Parts Over or 

Near Swimming Pools 1 

(Voltages are phase to ground for effectively grounded circuits and those other circuits where all ground 

faults are cleared by promptly de-energizing the faulted section, both initially and following subsequent 

breaker operations. See the definitions section for voltages of other systems. 

Clearances are with no wind displacement. 

See Rules 234E1, 234E2, and 234H4.) 





Insulated 

communication 

conductors and 

cables; 

messengers; 

surge- 
protection 
wires; grounded 
guys; 
ungrounded 
guys exposed to 

to 300 V 3 ; 

neutral 

conductors 

meeting Rule 

230E1; supply 

cables meeting 

Rule 230C1 

(ft) 


Unguarded rigid 
live parts, to 

750 V; 

noninsulated 

communication 

conductors; 

supply cables of 

to 750 V meeting 

Rules 230C2 or 

230C3; 
ungrounded guys 
exposed to open 

supply 

conductors of 

over 300 V to 

750 V 2 

(ft) 


Supply cables 

over 750 V 

meeting Rules 

230C2 or 
230C3; open 

i supply 
conductors, 
to 750 V 
(ft) 


Unguarded 

rigid live parts 

over 750 V to 

22 kV; 

ungrounded 
guys exposed 
to over 750 V 

to 22 kV 2 
(ft) 


Open 

supply 

conductors, 

over 750 V 

to 22 kV 

(ft) 


A. Clearance in any 
direction from the 
water level, edge of 
pool, base of diving 
platform, or anchored 
raft 


22.0 


22.5 


23.0 


24.5 


25.0 


B. Clearance in any 
direction to the diving 
platform or tower 


14.0 


14.5 


15.0 


16.5 


17.0 


V. Vertical clearance 
over adjacent land 


Clearance shall be as required by Rule 232. 



NOTE: A, B, and V are shown in Fig 234-3. 

1 The clearance values shown in this table are computed by adding the applicable Mechanical and Elec- 
trical (M & E) value of Table A-l to the applicable Reference Component of Table A- 2b of Appendix A. 

2 Ungrounded guys and ungrounded portions of guys between insulators shall have clearances based on 
the highest voltage to which they may be exposed due to a slack conductor or guy. 

Anchor guys insulated in accordance with Rule 279 may have the same clearance as grounded guys. 



114 
Copyright © 2001 IEEE. All rights reserved. 



234F 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



234F2c 



F. Clearances of Wires, Conductors, Cables, and Rigid Live Parts From Grain Bins 

1. Grain Bins Loaded by Permanently Installed Augers, Conveyers, or Elevator Systems 

All portions of grain bins that are expected to be loaded by the use of a permanently installed au- 
ger, conveyer, or elevator system shall be considered as a building or other installation under 
Rule 234C for the purpose of determining appropriate clearances of wires, conductors, cables, and 
rigid live parts. In addition, the following clearances shall also apply without wind displacement. 



Legend 
P = probe clearance 5.5 m (18 ft) required by 

Rule234F1a 
H = horizontal clearance 4.6 m (15 ft) required by 

Rule234F1b 
T = transition clearance 



Vj = Vertical clearance above a 
building required by Rule 
234C (Table 234-1) 

V 2 = Vertical clearance above land 
required by Rule 232C 




Dimension V] is determined by Rule 234C and Table 234-1, Row lb(2). 

Fig 234-4(a) 

Clearance Envelope for Grain Bins Filled by 

Permanently Installed Augers, Conveyors, or Elevators 



a. A clearance of not less than 5.5 m (18 ft) in all directions above the grain bin shall be main- 
tained from each probe port in the grain bin roof for all wires, conductors, and cables. 

b. A horizontal clearance of not less than 4.6 m (15 ft) shall be maintained between grain bins 
and open supply conductors, to 22 kV. 

Grain Bins Loaded by Portable Augers, Conveyers, or Elevators (With No Wind Displacement) 

a. The clearance of wires, conductors, cables, and rigid live parts from grain bins that are expect- 
ed to be loaded by the use of a portable auger, conveyer, or elevator shall be not less than the 
values illustrated in Fig 234-4b. 

EXCEPTION: Clearances of the following items on the nonloading side of grain bins shall be not less 
than those required by Rule 234C for clearances from buildings: 

( 1 ) Support arms ; effectively grounded equipment cases 

(2) Insulated communication conductors and cables, messengers, surge-protection wires, grounded 
guys, neutral conductors meeting Rule 230E1, and supply cables meeting Rule 230C1 

(3) Supply cables of to 750 V meeting Rules 230C2 or 230C3 

b. Any side of a grain bin is considered to be a nonloading side if it is so designated, or if it is so 
closely abutting another structure or obstruction, or so close to a public road or other right-of- 
way that a portable auger, conveyor, or elevator is not reasonably anticipated to be used over 
that side or portion to fill the grain bin. 

c. Where an agreement excludes the use of portable augers, conveyors, or elevators from a des- 
ignated portion of a grain bin, such portion is considered to be a nonloading side. 



115 
Copyright © 2001 IEEE. All rights reserved. 



F-234-4(b) 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



F-234-4(b) 




V = HEIGHT OF HIGHEST FILLING OR PROBING PORT ON GRAIN BIN 
H = V + 5.5m(18ft) 



LOADING SIDE 



RULE 232 AREA 




NON-LOADING SIDE 



4.6 m (15 ft) 



RULE 232 AREA 



AREA OF SLOPED 
CLEARANCE 



Fig 2344(b) 

Clearance Envelope for Grain Bins Filled by 

Portable Augers, Conveyors, or Elevators 



116 

Copyright © 2001 IEEE. All rights reserved. 



234G 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



234H3a 



G. Additional Clearances for Voltages Exceeding 22 kV for Wires, Conductors, Cables, and Unguarded 
Rigid Live Parts of Equipment 

Greater clearances than specified in Rules 234B, 234C, 234D, 234E, 234F, and 234J shall be provided 
where required below. 

1. For voltages between 22 and 470 kV, the clearance specified in Rules 234B, 234C, 234D, 234E, 
234F, and 234J shall be increased at the rate of 10 mm (0.4 in) per kV in excess of 22 kV. For 
voltages exceeding 470 kV, the clearance shall be determined by the method given in Rule 234H. 
All clearances for lines over 50 kV shall be based on the maximum operating voltage. 
EXCEPTION 1: Where a clearance value is given for the 22 kV to 50 kV range, the voltage adder of Rule 
234G1 applies to the voltage in excess of 50 kV. 

EXCEPTION 2: For voltages exceeding 98 kV ac to ground or 139 kV dc to ground, clearances less than 
those required above are permitted for systems with known maximum switching- surge factor. (See Rule 
234H.) 

2. For voltages exceeding 50 kV, the additional clearance specified in Rule 234G1 shall be increased 
3% for each 300 m (1000 ft) in excess of 1000 m (3300 ft) above mean sea level. 

3. For voltages exceeding 98 kV ac to ground, either the clearances shall be increased or the electric 
field, or the effects thereof, shall be reduced by other means, as required, to limit the steady-state 
current due to electrostatic effects to 5 mA, rms, if an ungrounded metal fence, building, sign, bill- 
board, chimney, radio or television antenna, tank or other installation, or any ungrounded metal 
attachments thereto, were short-circuited to ground. For this determination, the conductor shall be 
at a final unloaded sag at 50 °C (120 °F). 

H. Alternate Clearances for Voltages Exceeding 98 kV AC to Ground or 139 kV DC to Ground 

The clearances specified in Rules 234B, 234C, 234D, 234E, 234F, 234G, and 234J may be reduced 
for circuits with known switching-surge factors, but shall be not less than the alternate clearance, 
which is computed by adding the reference distance from Rule 234H2 to the electrical component of 
clearance from Rule 234H3. 

1. Sag Conditions of Line Conductors 

The vertical, horizontal, and diagonal clearances shall be maintained under the conductor temper- 
ature and loading conditions given in Rule 234A. 

2. Reference Distances 

The reference distance shall be selected from Table 234-5. 

3. Electrical Component of Clearance 

a. The electrical component (D) shall be computed using the following equations. Selected val- 
ues of D are listed in Table 234-4. 

„n 1.667 



I 



D = 1.00 



V(PU)-a 
500K 



be (m) 



D = 3.28 

where 
V 



V-(PU)a 
500K 



1.667 



(ft) 



maximum ac crest operating voltage to ground or maximum dc operating voltage 
to ground in kilovolts, 
PU = maximum switching-surge factor expressed in per-unit peak voltage to ground and 
defined as a switching- surge level for circuit breakers corresponding to 98% prob- 
ability that the maximum switching surge generated per breaker operation does not 
exceed this surge level, or the maximum anticipated switching-surge level gener- 
ated by other means, whichever is greater, 

a = 1.15, the allowance for three standard deviations, 

b = 1.03, the allowance for nonstandard atmospheric conditions, 

c = the margin of safety: 

1 .2 for vertical clearances 
1 .0 for horizontal clearances, 

K = 1.15, the configuration factor for conductor-to-plane gap. 

117 
Copyright © 2001 IEEE. All rights reserved. 



234H3b PART 2. SAFETY RULES FOR OVERHEAD LINES 234J2c 



b. The value of D shall be increased 3% for each 300 m (1000 ft) in excess of 450 m (1500 ft) 
above mean sea level. 
4. Limit 

The alternate clearance shall be not less than the clearance of Rule 234B, Table 234-1, 
Table 234-2, or Table 234-3, as applicable, computed for 98 kV ac rms to ground by Rule 
234G1. 

I. Clearance of Wires, Conductors, and Cables to Rail Cars 

Where overhead wires, conductors, or cables run along railroad tracks, the clearance in any direction 
shall be not less than that shown in Fig 234-5. The values of V and H are as defined below: 

V = vertical clearance from the wire, conductor, or cable above the top of the rail as spec- 
ified in Rule 232 minus 6.1 m (20 ft), the assumed height of the rail car 
H = horizontal clearance from the wire, conductor, or cable to the nearest rail, which is 
equal to the required vertical clearance above the rail minus 4.6 m (15 ft) as computed 
by the lesser of the following: 

1. Rules 232B1 and 232C1 

2. Rule232D 

These clearances are computed for railroads handling standard rail cars as common carriers in 
interchange service with other railroads. Where wires, conductors, or cables run along mine, 
logging, and similar railways that handle only cars smaller than standard freight cars, the value of 
H may be reduced by one-half the difference between the width of a standard rail car [3.3 m (10 ft, 
8 in)] and the width of the narrower car. 

J. Clearance of Equipment Mounted on Supporting Structures 

1. Clearance to Unguarded Rigid Live Parts of Equipment 

The horizontal and vertical clearances of unguarded rigid live parts such as potheads, transformer 
bushings, surge arresters, and short lengths of supply conductors connected thereto, which are not 
subject to variation in sag, shall be not less than those required by Rules 234C or 234D, as 
applicable. 

2. Clearance to Equipment Cases 

Equipment shall be mounted so that clearances are not less than that given by Rules 234J2a, 
234J2b, and 234J2c. 

a. Effectively grounded equipment cases may be located on or adjacent to buildings, bridges, or 
other structures provided that clearances for unguarded rigid live parts of such equipment, as 
specified in Rule 234J1, are maintained. 

b. Equipment cases that are not effectively grounded shall be located so that the clearances of 
Rules 234C or 234D, as applicable, are maintained. 

c. Equipment cases shall be located so as not to serve as a means of approach to unguarded rigid 
live parts by unqualified persons. 

NOTE: Rule 234J is not subject to the loading conditions of Rule 234A. 



118 
Copyright © 2001 IEEE. All rights reserved. 



F-234-5 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



F-234-5 




6.7 m 
(22 ft) 



> 
m 

o 
Lu 
cc 

o 

LU 

tx 

LU 
O 

z 
< 
cc 
< 

LU 



CM 

co 
eg 

LU 

_i 

CC 



Fig 234-5 
Rail Car Clearances 



119 
Copyright © 2001 IEEE. All rights reserved. 



T-234-4 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-234-4 



Table 234-4 
Electrical Component of Clearance of Buildings, Bridges, and Other Installations 

[Add 3% for each 300 m (1000 ft) in excess of 450 m (1500 ft) above mean sea level. 

See Rule 234H3a.] 



Maximum 

operating voltage 

phase to phase 

(kV) 


Switching- 
surge factor 
(per unit) 


Switching surge 

(kV) 


Electrical component of clearances 


Vertical 


Horizontal 


(m) 7/':'(ft) . 


(m) ■ : :-(ft), ; 


242 


2.0 


395 


0.82 ; 7 2.7 ■■':;.: 


0.70 |' : ..2.3,. 




2.2 


435 


0.98 3.2 


0.82 |: ",; 2,7. ■■ 




2.4 


474 


1.13 


37 

4.2 


0.94 ''■ ' ■ 3.i'7; 




2.6 


514 


1.28 


1.07 J .5.5 




2.8 


553 


1.40 4.S 


1.20 [ ' .'"4.Q. ' '; 




3.0 


593 


1.65 7-': '■■5,4 '/ 


1-40 ; : 4.5, , 


362 


1.8 


532 


1.40 


4 5 
5.4 


1.13 ..7 




2.0 


591 


1.65 


1 4(1 4.5 




2.2 


650 


1.90 


6.3 


1 .60 •■• 2 




2.4 


709 


2.20 


7.1 


1.85 . ..' : . -6.1 ■ ■■■ 




2.6 


768 


2.50 


8.3 


2.10 6.9 

i" ■ . 




2.8 


828 


2.90 


9.4 


2-40 | '7.8-V . 




3.0 


887 


3.2 


106 


: 70 8.8 


550 


1.6 


719 


2.30 


7.5 


1.90 : , " ;'6.2 : ■ 




1.8 


808 


2.80 


l ».i 


2.30 7.6 




2.0 


898 


3.3 


10.8 


2.70 9.0 




2.2 


988 


3.9 


12.7 


3.2 : ?. 1.0,6- - '.■ 




2.4 


1079 


4.4 


14.6 


3.7 12.2 




2.6 


1168 


5.1 


16 7 


4.2 ■■;■/'. 13.9 : ..':- 


800 


1.6 


1045 


4.2 


13.9 


3-5 ('■■''■ 11.6 . .'■ 




1.8 


1176 


5.2 


16.9 


4-3 [ :. .14.1. ' ': 




2.0 


1306 


6.1 


20 1 


5.1 16.7 




2.2 


1437 


7.2 ^ 23,6/ /. 


6.0 j'. . 1.9.7/'. 




2.4 


1568 


8.3 27.3 


6.9 [■ ■. 22.7 ■ : 



120 
Copyright © 2001 IEEE. All rights reserved. 



T-234-5 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



235B1 



Table 234-5 
Reference Distances 

(See Rule 234H2.) 



Reference distance 


Vertical 


Horizontal 


(m) 


■ ft) 


(m) 


: (ft) 


a. Buildings 


2.70 


Q 


0.90 


: :.$'■; ' 


b. Signs, chimneys, radio and television antennas, tanks, and 
other installations not classified as bridges or buildings 


2.70 


9 


0.90 


3 


1,2 

c. Superstructure of bridges 


2.70 


9 


0.90 


■: . -.'3-. '.' 


d. Supporting structures of another line 


1.80 ft 


1.50 


■ :■: 5 : : ■: 


e. Dimension A of Fig 234-2 


5.5 : '' 18 


— 


:-._■.; 


f. Dimension B of Fig 234-2 


4.3 14 


4.3 


:■' "14; . ■ 



* Where over traveled ways on or near bridges, the clearances of Rule 232 apply also. 

2 Where the bridge has moving parts, such as a lift bridge, the required clearances shall be maintained 
throughout the full range of movement of the bridge or any attachment thereto. 

235. Clearance for Wires, Conductors, or Cables Carried on the Same Supporting Structure 

A. Application of Rule 

1 . Multiconductor Wires or Cables 

Cables, and duplex, triple, or paired conductors supported on insulators or messengers meeting 
Rules 230C or 230D, whether single or grouped, for the purposes of this rule are considered single 
conductors even though they may contain individual conductors not of the same phase or polarity. 

2. Conductors Supported by Messengers or Span Wires 

Clearances between individual wires, conductors, or cables supported by the same messenger, or be- 
tween any group and its supporting messenger, or between a trolley feeder, supply conductor, or 
communication conductor, and their respective supporting span wires, are not subject to the provi- 
sions of this rule. 

3. Line Conductors of Different Circuits 

a. Unless otherwise stated, the voltage between line conductors of different circuits shall be the 
greater of the following: 

(1) The phasor difference between the conductors involved 

NOTE: A phasor relationship of 180° is considered appropriate where the actual phasor relationship is 
unknown. 

(2) The phase-to-ground voltage of the higher- voltage circuit. 

b. When the circuits have the same nominal voltage, either circuit may be considered to be the high- 
er-voltage circuit. 

B. Horizontal Clearance Between Line Conductors 
1. Fixed Supports 

Line conductors attached to fixed supports shall have horizontal clearances from each other not less 
than, the larger value required by either Rule 235Bla or Rule 235Blb for the situation concerned. 
Voltage is between the two conductors for which the clearance is being determined except for rail- 
way feeders, which are to ground. 

EXCEPTION 1: The pin spacing at buckarm construction may be reduced as specified in Rule 236F to provide 
climbing space. 

EXCEPTION 2: Grades D and N need meet only the requirements of Rule 235B la. 

EXCEPTION 3: These clearances do not apply to cables meeting Rule 230C or covered conductors of the same 
circuit meeting Rule 230D. 

EXCEPTION 4: For voltages to ground exceeding 98 kV ac or 139 kV dc, clearances less than those required 
by a and b below are permitted for systems with known maximum switching-surge factors. (See Rule 235B3.) 



1 



121 
Copyright © 2001 IEEE. All rights reserved. 



235B la PART 2. SAFETY RULES FOR OVERHEAD LINES 235B lb 



Horizontal Clearance Between Line Conductors of the Same or Different Circuits 
Clearances shall be not less than those given in Table 235-1 . 
Clearance According to Sags 

The clearance at the supports of conductors of the same or different circuits of Grade B or C 
in no case shall be less than the values given by the following formulas, at a conductor tem- 
perature of 15 °C (60 °F), at final unloaded sag, no wind. The requirements of Rule 235Bla 
apply if they give a greater separation than this rule. 

EXCEPTION: No requirement is specified for clearance between conductors of the same circuit when 
rated above 50 kV. 

In the following, 5 is the apparent sag in inches of the conductor having the greater sag, 
and the clearance is in inches. 

(1) For line conductors smaller than AWG No. 2: clearance = 0.3 inches per kilovolt + 

4.04 75-24 . (Table 235-2 shows selected values up to 46 kV.) 

(2) For line conductors of AWG No. 2 or larger: clearance = 0.3 inches per kilovolt + 
875/ 12 . (Table 235-3 shows selected values up to 46 kV.) 

(3) For voltages exceeding 8 14 kV, the clearance shall be determined by the alternate method 
given by Rule 235B3. 

In the following, S is the apparent sag in millimeters of the conductor having the greater 
sag, and the clearance is in millimeters. 



(1) For line conductors smaller than AWG No. 2: clearance = 7.6(kV) + 20.4 Js -610. 
(Table 235-2 shows selected values up to 46 kV.) 

(2) For line conductors of AWG No. 2 or larger: clearance = 7.6(kV) + 8 7(2.125) . 
(Table 235-3 shows selected values up to 46 kV.) 

(3) For voltages exceeding 8 14 kV, the clearance shall be determined by the alternate method 
given by Rule 235B3. 

(4) The clearance for voltages exceeding 50 kV specified in Rule 235Blb(l) and (2) shall be 
increased 3% for each 300 mm(1000 ft) in excess of 1000 m (3300 ft) above mean sea 
level. All clearances for lines over 50 kV shall be based on the maximum operating 
voltage. 



122 
Copyright © 2001 IEEE. All rights reserved. 



T-235-1 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-235-1 



Table 235-1 
Horizontal Clearance Between Wires, Conductors, or Cables at Supports 

(All voltages are between conductors involved except for railway feeders, which are to ground. 
See also Rules 235 A, 235B3b, and 235Bla.) 



Class of circuit 


Clearance 


Notes 


(mm) 


(in) 


Open communication conductors 


150 


fi 


Does not apply at conductor 
transposition points. 




75 


■:.-.. 3 

'■■ -\ : .i'..:6 ■'■-:■"■. ■■' 

■ . .■ 12-: '■■ '■ 

:■■■-;.-. n \ ■:'.'.:■': 


Permitted where pin spacings 
less than 150 mm (6 in) have 
been in regular use. Does not 
apply at conductor 
transposition points. 


Railway feeders: 

to 750 V, AWG No. 4/0 or larger 
to 750 V, smaller than AWG No. 4/0 
Over 750 V to 8.7 kV 


150 
300 
300 


Where 250 to 300 mm (10 to 
12 in) clearance has already 
been established by practice, 
it may be continued, subject 
to the provisions of Rule 
235Blb, for conductors 
having apparent sags not over 
900 mm (3 ft) and for 
voltages not exceeding 
8.7 kV. 


Supply conductors of the same circuit: 
to 8.7 kV 
Over 8.7 to 50 kV 

Above 50 kV 


300 
300 plus 10 per kV 

over 8.7 kV 
no value specified 


l- 
P phis ii l |n-r kV 

over 8.7 kV 
no \al Ik" spci ilicd 

■ : -|2 '■■■■:■ 
12 plus 0.4 per kV 

...'.v. S. / kV 

28.5 nlus 0.4 per kV 

over 50 k V 




Supply conductors of different circuits: 
to 8.7 kV 
Over 8.7 to 50 kV 

Over50kVto814kV 


300 
300 plus 10 per kV 

over 8.7 kV 
725 plus 10 per kV 

over 50 kV 


For all voltages above 50 kV, 
the additional clearance shall 
be increased 3% for each 
300 m (1000 ft) in excess of 
1000 m (3300 ft) above mean 
sea level. All clearances for 
voltages above 50 kV shall be 
based on the maximum 
operating voltage. 



123 
Copyright © 2001 IEEE. All rights reserved. 



T-235-2(m) 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-235-2(in) 



m 



Table 235-2 

Horizontal Clearances Between Line Conductors 

Smaller Than AWG No. 2 at Supports, Based on Sags 

(See also Rule 235B lb.) 



Voltage 

between 

conductors 

(kV) 


Sag (mm) 


915 


1220 


1830 


2440 


3050 


4570 


6095 


But 

not 

less 

than 1 


Horizontal clearance (mm) 


2.4 


375 


520 


730 


890 


1025 


1300 


1525 


300 


4.16 


390 


535 


745 


905 


1040 


1315 


1540 


300 


12.47 


450 


595 


805 


965 


1100 


1375 


1605 


345 


13.2 


455 


605 


810 


970 


1105 


1385 


1610 


350 


13.8 


460 


605 


815 


975 


1110 


1385 


1615 


355 


14.4 


465 


610 


820 


980 


1115 


1390 


1620 


365 


24.94 


545 


695 


900 


1060 


1195 


1475 


1700 


470 


34.5 


620 


765 


975 


1135 


1270 


1545 


1775 


570 


46 


705 


855 


1060 


1220 


1355 


1635 


1860 


685 



Clearance determined by Table 235-1, Rule 235Bla. 
NOTE: Clearance = 7.6 (kV) + 20.4 Js - 610 , where S is the sag in millimeters. 



Table 235-2 

Horizontal Clearances Between Line Conductors 

Smaller Than AWG No. 2 at Supports, Based on Sags 

(See also Rule 235B lb.) 



Clearance determined by Table 235-1, Rule 235Bla. 
NOTE: Clearance = 0.3 (kV) + 4.04 JS- 24 , where S is the sag in inches. 



in 



Voltage 

between 

conductors 

(kV) 


Sag (in) 


36 


48 


72 


96 


120 


180 


240 


But 

not 

less 

than 1 


Horizontal clearance (in) 


2.4 


14.7 


20.5 


28.7 


35.0 


40.3 


51.2 


60.1 


12.0 


4.16 


15.3 


21.1 


29.3 


35.6 


40.9 


51.8 


60.7 


12.0 


12.47 


17.7 


23.5 


31.7 


38.0 


43.3 


54.2 


63.1 


13.5 


13.2 


18.0 


23.8 


32.0 


38.3 


43.6 


54.5 


63.4 


13.8 


13.8 


18.1 


23.9 


32.1 


38.4 


43.7 


54.6 


63.5 


14.0 


14.4 


18.3 


24.1 


32.3 


38.6 


43.9 


54.8 


63.7 


14.3 


24.94 


21.5 


27.3 


35.5 


41.8 


47.1 


58.0 


66.9 


18.5 


34.5 


24.4 


30.2 


38.4 


44.7 


50.0 


60.9 


69.8 


22.4 


46 


27.8 


33.6 


41.8 


48.1 


53.4 


64.3 


73.2 


26.9 



124 
Copyright © 2001 IEEE. All rights reserved. 



T-235-3(m) 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-235-3(in) 



m 



Table 235-3 

Horizontal Clearances Between Line Conductors 

AWG No. 2 or Larger at Supports, Based on Sags 

(See also Rule 235B lb.) 



Voltage 

between 

conductors 

(kV) 


Sag (mm) 


915 


1220 


1830 


2440 


3048 


4572 


6096 


But 

not 

less 

than 1 


Horizontal clearance (mm) 


2.4 


370 


425 


515 


590 


660 


805 


925 


300 


4.16 


385 


440 


530 


605 


675 


820 


940 


300 


12.47 


445 


500 


600 


670 


735 


880 


1005 


345 


13.2 


450 


510 


595 


675 


740 


885 


1010 


350 


13.8 


455 


510 


600 


680 


745 


890 


1015 


355 


14.4 


460 


515 


605 


685 


750 


895 


1020 


365 


24.94 


540 


595 


685 


760 


835 


975 


1100 


470 


34.5 


615 


670 


760 


835 


905 


1050 


1170 


570 


46 


705 


755 


845 


925 


995 


1140 


1260 


685 



Clearance determined by Table 235-1, Rule 235Bla. 
NOTE: Clearance = 7.6 (kV) + &J2.12S , where S is the sag in millimeters. 



Table 235-3 
Horizontal Clearances Between Line Conductors 
AWG No. 2 or Larger at Supports, Based on Sags 

(See also Rule 235B lb.) 



1 Clearance determined by Table 235-1, Rule 235Bla. 
NOTE: Clearance = 0.3 (kV) + 875/12 , where S is the sag in inches. 



I 



in 



Voltage 

between 

conductors 

(kV) 


Sag (in) 


36 


48 


72 


96 


120 


180 


240 


But 

not 

less 

than 1 


Horizontal clearance (in) 


2.4 


14.6 


16.7 


20.2 


23.3 


26.0 


31.7 


36.5 


12.0 


4.16 


15.1 


17.3 


20.8 


23.8 


26.5 


32.2 


37.0 


12.0 


12.47 


17.6 


19.7 


23.3 


26.3 


29.0 


34.7 


39.5 


13.5 


13.2 


17.8 


20.0 


23.5 


26.5 


29.2 


34.9 


39.7 


13.8 


13.8 


18.0 


20.1 


23.7 


26.7 


29.4 


35.1 


39.9 


14.0 


14.4 


18.2 


20.3 


23.8 


26.9 


29.6 


35.3 


40.1 


14.3 


24.94 


21.3 


23.5 


27.0 


30.0 


32.8 


38.4 


43.2 


18.5 


34.5 


24.2 


26.4 


29.9 


32.9 


35.6 


41.3 


46.1 


22.4 


46 


27.7 


29.8 


33.3 


36.4 


39.1 


44.8 


49.6 


26.9 



125 
Copyright © 2001 IEEE. All rights reserved. 



235B2 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



235C 



2. Suspension Insulators 

Where suspension insulators are used and are not restrained from movement, the clearance be- 
tween conductors shall be increased so that one string of insulators may swing transversely 
throughout a range of insulator swing up to its maximum design swing angle without reducing the 
values given in Rule 235B1. The maximum design swing angle shall be based on a 290 Pa (6 lb/ 
ft 2 ) wind on the conductor at final sag at 15 °C (60 °F). This may be reduced to a 190 Pa (4 lb/ft 2 ) 
wind in areas sheltered by buildings, terrains, or other obstacles. The displacement of the wires, 
conductors, and cables shall include deflection of flexible structures and fittings, where such de- 
flection would reduce the horizontal clearance between two wires, conductors, or cables. 

3. Alternate Clearances for Different Circuits Where One or Both Circuits Exceed 98 kV AC to 
Ground or 139 kV DC to Ground 

The clearances specified in Rules 235B1 and 235B2 may be reduced for circuits with known 
switching-surge factors but shall be not less than the clearances derived from the following com- 
putations. For these computations, communication conductors and cables, guys, messengers, neu- 
tral conductors meeting Rule 230E1, and supply cables meeting Rule 230C1 shall be considered 
line conductors at zero voltage, 
a. Clearance 

(1) The alternate clearance shall be maintained under the expected loading conditions and 
shall be not less than the electrical clearance between conductors of different circuits 
computed from the following equation. For convenience, clearances for typical system 
voltages are shown in Table 235-4. 



D = 1.00 



= 3.28 



V L _ L (PU) -a-, 1.667 




1.667 



(m) 



(ft) 



L-L 



PU = 



where 

maximum ac crest operating voltage in kilovolts between phases of different 
circuits or maximum dc operating voltage between poles of different circuits. 
If the phases are of the same phase and voltage magnitude, one phase conduc- 
tor shall be considered grounded, 

maximum switching-surge factor expressed in per-unit peak operating voltage 
between phases of different circuits and defined as a switching-surge level be- 
tween phases for circuit breakers corresponding to 98% probability that the 
maximum switching surge generated per breaker operation does not exceed 
this surge level, or the maximum anticipated switching-surge level generated 
by other means, whichever is greater, 
1.15, the allowance for three standard deviations, 

1.03, the allowance for nonstandard atmospheric conditions, 

1.4, the configuration factor for a conductor-to-conductor gap. 
The value of D shall be increased 3% for each 300 m (1000 ft) in excess of 450 m (1500 ft) 
above mean sea level. 

b. Limit 

The clearance derived from Rule 235B3a shall not be less than the basic clearances given in 
Table 235-1 computed for 169 kV ac. 



a 
b 
K 



(2) 



C. Vertical Clearance Between Line Conductors 

All line wires, conductors, and cables located at different levels on the same supporting structure shall 
have vertical clearances not less than the following: 



126 
Copyright © 2001 IEEE. All rights reserved. 



235C1 PART 2. SAFETY RULES FOR OVERHEAD LINES 235C2b(l)(b) 



1 . Basic Clearance for Conductors of Same or Different Circuits 

The clearances given in Table 235-5 shall apply to line wires, conductors, or cables of to 50 kV 

attached to supports. No value is specified for clearances between conductors of the same circuit 

exceeding 50 kV. 

EXCEPTION 1: Line wires, conductors, or cables on vertical racks or separate brackets placed vertically and 

meeting the requirements of Rule 235G may have spacings as specified in that rule. 

EXCEPTION 2: Where communication service drops cross under supply conductors on a common crossing 

structure, the clearance between the communication conductor and an effectively grounded supply conductor 

may be reduced to 100 mm (4 in) provided the clearance between the communication conductor and supply 

conductors not effectively grounded meets the requirements of Rule 235C as appropriate. 

EXCEPTION 3: Supply service drops of to 750 V running above and parallel to communication service drops 

may have a spacing of not less than 300 mm ( 1 2 in) at any point in the span including the point of their attachment 

to the building or structure being served provided that the nongrounded conductors are insulated and that the 

clearance as otherwise required by this rule is maintained between the two service drops at the pole. 

EXCEPTION 4: This rule does not apply to conductors of the same circuit meeting Rule 230D. 

2. Additional Clearances 

j Greater clearances than those required (by Rule 235C1) and given in Table 235-5 shall be provided 

under the following conditions. The increases are cumulative where more than one is applicable. 

a. Voltage Related Clearances 

1(1) For voltages between 50 and 814 kV, the clearance between line wires, conductors, or ca- 
bles of different circuits shall be increased 10 mm (0.4 in) per kilovolt in excess of 50 kV. 
EXCEPTION: For voltages to ground exceeding 98 kV ac or 139 kV dc, clearances less than those 
required above are permitted for systems with known switching-surge factors. (See Rule 235C3.) 

(2) The increase in clearance for voltages in excess of 50 kV specified in Rule 235C2a(l) shall 
be increased 3% for each 300 m (1000 ft) in excess of 1000 m (3300 ft) above mean sea 
level. 

(3) All clearances for lines over 50 kV shall be based on the maximum operating voltage. 

(4) No value is specified for clearances between conductors of the same circuit. 

b. Sag-Related Clearances 

| (1) Line wires, conductors, and cables supported at different levels on the same structures shall 

have vertical clearances at the supporting structures so adjusted that the clearance at any 
point in the span shall be not less than any of the following: 



I 



I 



(a) For voltages less than 50 kV between conductors, 75% of that required at the supports 
by Table 235-5. 

EXCEPTION 1: Neutral conductors meeting Rule 230E1 and supply cables meeting Rule 230C1 
(including their support brackets) running above and parallel to communication cables where the 
supply neutral or messenger is bonded to the communication messenger at intervals specified in 
Rule 92C, may have a clearance of 300 mm (12 in) at any point in the span provided that a 
clearance of 0.75 m (30 in) is maintained between the supply conductors and cables and the 
communication cables at the supporting poles. 

EXCEPTION 2: When all parties involved are in agreement, for supply conductors of different 
utilities, vertical clearance at any point in the span need not exceed 75% of the values required 
at the supports for the same utility by Table 235-5. 

(b) For voltages more than 50 kV between conductors, the value specified in Rule 
235C2b(l)(a) increased in accordance with Rule 235C2a. 



127 
Copyright © 2001 IEEE. All rights reserved. 



T-235-4 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-235-4 



Table 235-4 
Electrical Clearances in Rule 235B3a(l) 

[Add 3% for each 300 m (1000 ft) in excess of 450 m (1500 ft) above mean sea level.] 



Maximum 

operating voltage 

phase to phase 

(kV) 


Switching 

surge factor 

(per unit) 


Switching 
surge 

(kV) 


Electrical component of clearance 


(m) ■ '■':■'. ' M\ '.'::■: ■ 


242 


2.6 or less 


890 or less 


1.90 


■■■/■■■:. -S3 1 ; ■■■.:■■■: 




2.8 


958 


2.20 


.."''■■;'■■ 7:2'.;.; ; :;' 




3.0 


1027 


2.50 


''■'■'" ■'"'s.i~- ■■:'_■■ ~ 

8.8 2 




3.2 or more 


1095 or more 


2.70 


362 


1.8 


893 or less 


1.95 


, ,; 1 




2.0 


1024 


2.45 


'.'■':'■■■'■ -8.0.. '. : : '."■'' 

9.5 
'■ ■: ■' ' K).9 ; ■ ■. ' 
'. ! ■ : " 12.5 : 
::\. : ; ;' 12:8. ? ;".-. '■-'■.;:;'. 




2.2 


1126 


2.90 




2.4 


1228 


3.3 




2.6 


1330 


3.8 




2.7 or more 


1382 or more 


3.9 


550 


1.6 


1245 


3.4 


: :. :';..': \n,2';-'- ■';':'; y. 




1.8 


1399 


4.1 


; ■':'.-: '■:■ 1X6 ■■■■■ y : ;. 
! 9 




2.0 


1555 


4.9 




2.2 


1711 


5.8 




2.3 


1789 or more 


5.8 


x : ;': ; ::19.1 2: . ■ .... 


800 


1.6 


1810 


6.3 


■'-.;: ..';''. '20.8-.. .■ ■';. ■ ■ 
'■■■]■■ ■ : :''?.5',3". ■ '■.' 

27 4 - 




1.8 


2037 


7.7 




1.9 or more 


2149 or more 


8.4 



1 Limited by Rule 235B3b. 

2 Need not be greater than specified in Rules 235B1 and 235B2. 



128 
Copyright © 2001 IEEE. All rights reserved. 



T-235-5(m) 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-235-5(m) 



m 

Table 235-5 
Vertical Clearance Between Conductors at Supports 

(When using column and row headings, voltages are phase to ground for effectively grounded circuits and 

those other circuits where all ground faults are cleared by promptly de-energizing the faulted section, both 

initially and following subsequent breaker operations. See the definitions section for voltages of other 

systems. See also Rules 235C1, 235C2, and 235F.) 



Conductors and cables 
usually at lower levels 


Conductors and cables usually at upper levels 


Supply cables 
meeting Rule 230C1, 

2, or 3; neutral 

conductors meeting 

Rule 230E1; 

communications 

cables meeting Rule 

224A2a 

(m) 


Open supply conductors 


Oto 
8.7 kV 

(m) 


Over 8.7 to 50 kV 


Same utility 7 
(m) 


Different 

utilities 8 

(m) 


1. Communication conductors and 
cables 










a. Located in the communication 
space 


1.00 1>5 


1.00 


1.00 


1.00 plus 0.01 

per kV 6 
over 8.7 kV 


b. Located in the supply space 


0.419.10 


0.41 10 


LOO 10 


1.00 plus 0.01 

perkV 6 
over 8.7 kV 


2. Supply conductors and cables 










a. Open conductors to 750 V; 
supply cables meeting Rule 230C1, 2, 
or 3; neutral conductors meeting Rule 
230E1 


0.41 9 


0.41 2 


0.41 plus 0.01 

perkV 6 
over 8.7 kV 


1.00 plus 0.01 

perkV 6 
over 8.7 kV 


b. Open conductors over 750 V to 

8.7 kV 




0.41 2 


0.41 plus 0.01 
perkV 4 - 6 
over 8.7 kV 


1.00 plus 0.01 
per kV A 6 
over 8.7 kV 


c. Open conductors over 8.7 to 
22 kV 










(1) If worked on energized with 
live-line tools and adjacent circuits 
are neither de-energized nor covered 
with shields or protectors 






0.41 plus 0.01 

per kV 6 
over 8.7 kV 


1.00 plus 0.01 

perkV 6 
over 8.7 kV 


(2) If not worked on energized 
except when adjacent circuits (either 
above or below) are de-energized or 
covered by shields or protectors, or by 
the use of live-line tools not requiring 
line workers to go between live wires 






0.41 plus 0.01 
perkV 3 - 6 
over 8.7 kV 


0.41 plus 0.01 
perkV 3 - 6 
over 8.7 kV 


d. Open conductors exceeding 
22 kV, but not exceeding 50 kV 






0.41 plus 0.01 
perkV 3 ' 6 
over 8.7 kV 


0.41 plus 0.01 
perkV 3 - 6 
over 8.7 kV 



I 



129 
Copyright © 2001 IEEE. All rights reserved. 



T-235-5(m) PART 2. SAFETY RULES FOR OVERHEAD LINES T-235-5(m) 



1 Where supply circuits of 600 V or less, with transmitted power of 5000 W or less, are run below 
communication circuits in accordance with Rule 220B2, the clearance may be reduced to 0.41 m. 

| 2 Where conductors are operated by different utilities, a vertical clearance of not less than 1.00 m is 
recommended. 

I ■* These values do not apply to conductors of the same circuit or circuits being carried on adj acent conductor 

supports. 

I 4 May be reduced to 0.41 m where conductors are not worked on energized except when adjacent circuits 
(either above or below) are de-energized or covered by shields or protectors, or by the use of live-line tools 
not requiring line workers to go between live wires. 

I 5 May be reduced to 0.75 m for supply neutrals meeting Rule 230E1, entirely dielectric fiber-optic supply 
cables meeting Rule 230Flb and cables meeting Rule 230C1 where the supply neutral or messenger is bonded 
to the communication messenger. 

I ° The greater of phasor difference or phase-to-ground voltage; see Rule 235A3. 
' Example: For a 50 kV-to-ground conductor above a 22 kV-to-ground conductor, the required clearance 
is 0.41 m + 0.64 m = 1.05 m when the conductors are 180° out of phase. 

I ° Example: For a 50 kV-to-ground conductor above a 22 kV-to-ground conductor, the required clearance 
is 1.00 m + 0.64 m = 1.64 m when the conductors are 180° out of phase. 

" No clearance is specified between neutral conductors meeting Rule 230E1 and insulated communication 
cables located in the supply space and supported by an effectively grounded messenger. 

No clearance is specified between fiber-optic — supply cables meeting Rule 230Flb and supply cables 
and conductors. 



130 
Copyright © 2001 IEEE. All rights reserved. 



T-235-5(in) 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-235-5(in) 



in 

Table 235-5 
Vertical Clearance Between Conductors at Supports 

(When using column and row headings, voltages are phase to ground for effectively grounded circuits and 

those other circuits where all ground faults are cleared by prompdy de-energizing the faulted section, both 

initially and following subsequent breaker operations. 

See the definitions section for voltages of other systems. 

See also Rules 235C1, 235C2, and 235F.) 



Conductors and cables 
usually at lower levels 


Conductors and cables 
usually at upper levels 


Supply cables 

meeting Rule 

230C1, 2, or 3,- 

neutral conductors 

meeting Rule 

230E1; 

communications 

cables meeting 

Rule 224A2a 

(in) 


Open supply conductors 


Oto 

8.7 kV 

(in) 


Over 8.7 to 50 kV 


Same utility 7 

(in) 


Different 

utilities 8 

(in) 


1. Communication conductors and 
cables 










a. Located in the communication 
space 


40 1.5 


40 


40 


40 plus 0.4 

perkV 6 
over 8.7 kV 


b. Located in the supply space 


16 9,10 


16 10 


40 10 


40 plus 0.4 

per kV 6 

over 8.7 kV 


2. Supply conductors and cables 










a. Open conductors to 750 V; 
supply cables meeting Rule 230C1, 2, 
or 3; neutral conductors meeting Rule 
230E1 


16 9 


16 2 


16 plus 0.4 

per kV 6 

over 8.7 kV 


40 plus 0.4 

per kV 6 
over 8.7 kV 


b. Open conductors over 750 V to 
8.7 kV 




16 2 


16 plus 0.4 

per kV 4 - 6 
over 8.7 kV 


40 plus 0.4 

perkV 6 

over 8.7 kV 


c. Open conductors over 8.7 to 
22 kV 










(1) If worked on energized with 
live-line tools and adjacent circuits 
are neither de-energized nor covered 
with shields or protectors 






16 plus 0.4 

perkV 6 

over 8.7 kV 


40 plus 0.4 

perkV 6 

over 8.7 kV 


(2) If not worked on energized 
except when adjacent circuits (either 
above or below) are de-energized or 
covered by shields or protectors, or by 
the use of live-line tools not requiring 
line workers to go between live wires 






16 plus 0.4 
per kV 3 ' 6 
over 8.7 kV 


16 plus 0.4 
perkV 3 ' 6 
over 8.7 kV 


d. Open conductors exceeding 
22 kV, but not exceeding 50 kV 






16 plus 0.4 
per kV 3 ' 6 
over 8.7 kV 


16 plus 0.4 
perkV 3 ' 6 
over 8.7 kV 



I 



131 
Copyright © 2001 IEEE. All rights reserved. 



T-235-5(in) PART 2. SAFETY RULES FOR OVERHEAD LINES T-235-5(in) 



1 Where supply circuits of 600 V or less, with transmitted power of 5000 W or less, are run below commu- 
nication circuits in accordance with Rule 220B2, the clearance may be reduced to 16 in. 

I 2 Where conductors are operated by different utilities, a vertical clearance of not less than 40 in is recom- 
mended. 

| 3 xhese values do not apply to conductors of the same circuit or circuits being carried on adj acent conductor 
supports. 

| 4 May be reduced to 16 in where conductors are not worked on energized except when adjacent circuits 
(either above or below) are de-energized or covered by shields or protectors, or by the use of live line tools 
not requiring line workers to go between live wires. 

I-* May be reduced to 30 in for supply neutrals meeting Rule 230E1, entirely dielectric fiber-optic supply 
cables meeting Rule 230Flb, and cables meeting Rule 230C1 where the supply neutral or messenger is bond- 
ed to the communication messenger. 

I" The greater of phasor difference or phase-to-ground voltage; see Rule 235A3. 
' Example: For a 50 kV-to-ground conductor above a 22 kV-to-ground conductor, the required clearance 
is 16 in [+] 25 in [=] 41 in when the conductors are 180° out of phase. 

[ ° Example: For a 50 kV-to-ground conductor above a 22 kV-to-ground conductor, the required clearance 
is 40 in [+] 25 in [=] 65 in when the conductors are 180° out of phase. 

No clearance is specified between neutral conductors meeting Rule 230E1 and insulated communication ca- 
bles located in the supply space and supported by an effectively grounded messenger. 

10 No clearance is specified between fiber-optic — supply cables meeting Rule 230Flb and supply cables 
and conductors. 



132 
Copyright © 2001 IEEE. All rights reserved. 



235C2b(l)(c) PART 2. SAFETY RULES FOR OVERHEAD LINES 235C4 



(c) For purposes of this determination the vertical clearances required in Rule 
235C2b(l)(a) and (b) apply to the following conductor temperature and loading con- 
ditions whichever produces the greater vertical clearance at the structure when: 
i. The upper conductor is at final sag at the maximum operating temperature for 
which the line is designed to operate and the lower conductor is at final sag at the 
same ambient conditions as the upper conductor without electrical loading, and 
without ice loading, or 
ii. The upper conductor is at final sag at 32 °F with the radial thickness of ice, if any, 
specified in Rule 250B for the loading district concerned and the lower conductor 
is at final sag at the same ambient conditions as the upper conductor without elec- 
trical loading, and without ice loading. 
EXCEPTION: Rule 235C2b(l)(c) does not apply to conductors of the same utility when the 
conductors are the same size and type, and are installed at the same sag and tension. However, 
where experience in an area has shown that different ice conditions do occur between the upper 
and lower conductors, then Rule 235C2b(l)(c) shall apply. 

(2) Sags should be readjusted when necessary to accomplish the foregoing, but not reduced 
sufficiently to conflict with the requirements of Rule 261H2. In cases where conductors 
of different sizes are strung to the same sag for the sake of appearance or to maintain un- 
reduced clearance throughout storms, the chosen sag should be such as will keep the 
smallest conductor involved in compliance with the sag requirements of Rule 261H2. 

(3) For span lengths in excess of 45 m (150 ft), vertical clearance at the structure between 
open supply conductors and communication cables or conductors shall be adjusted so that 
under conditions of conductor temperature of 15 °C (60 °F), no wind displacement and 
final unloaded sag, no open supply conductor of over 750 V but less than 50 kV shall be 
lower in the span than a straight line joining the points of support of the highest commu- 
nication cable or conductor. 

EXCEPTION: Effectively grounded supply conductors associated with systems of 50 kV or less 
need meet only the provisions of Rule 235C2b(l). 

3. Alternate Clearances for Different Circuits Where One or Both Exceed 98 kV AC, or 139 kV DC 
to Ground 

The clearances specified in Rules 235C1 and 235C2 may be reduced for circuits with known 
switching-surge factors, but shall not be less than the crossing clearances required by Rule 233C3. 

4. Communication Worker Safety Zone 

The clearance specifications of Rules 235C and 238 create a communication worker safety zone 
between the facilities located in the supply space and facilities located in the communication 
space, both at the structure and in the span between structures. Except as allowed by Rules 238C, 
238D, and 239, no supply or communication facility shall be located in the communication worker 
safety zone. 



133 
Copyright ©2001 IEEE. All rights reserved. 



235D 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



F-235-1 



D. Diagonal Clearance Between Line Wires, Conductors, and Cables Located at Different Levels on the 
Same Supporting Structure 

No wire, conductor, or cable may be closer to any other wire, conductor, or cable than defined by the 
dashed line in Fig 235- 1 , where V and H are determined in accordance with other parts of Rule 235. 



>— H ■!■ h- 




-,--> 



V = Vertical clearance 
H = Horizontal clearance 

Fig 235-1 
Clearance Diagram for Energized Conductor 



134 
Copyright © 2001 IEEE. All rights reserved. 



T-235-6(m) 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-235-6(m) 



m 



Table 235-6 

Clearance in Any Direction From Line Conductors to Supports and to 

Vertical or Lateral Conductors, Span, or Guy Wires Attached to the Same Support 

[See also Rule 235E1, 235E3b(2), and 2351.] 



Clearance of line 
conductors from 


Communication lines 


Supply lines 
Circuit phase-to-phase voltage 


In general 
(mm) 


On jointly 

used 
structures 

(mm) 


Oto 
8.7 kV 
(mm) 


Over 8.7 

to SO kV 

(mm) 


Over 50 

to814kV 4 ' 9 

(mm) 


1. Vertical and lateral conductors: 












a. Of the same circuit 


75 


75 


75 


75 plus 6.5 

perkV 
over 8.7 kV 


no value specified 


b. Of other circuits 12 ' 13 


75 


75 


150 5 


150 plus 10 

perkV 
over 8.7 kV 


580 plus 10 

per kV 
over 50 kV 


2. Span or guy wires, 11 or 
messengers attached to same 
structure: 












a. When parallel to line 


75 7 


150 1 ' 7 


300 1 


300 plus 10 

perkV 
over 8.7 kV 


740 plus 10 

perkV 
over 50 kV 


b. Anchor guys 


75 7 


150 1 - 7 


150 1 


150 plus 6.5 per 
kV over 8.7 kV 


410 plus 6.5 

perkV 
over 50 kV 


c. All other 


75 7 


150 1 - 7 


150 


150 plus 10 per 
kV over 8.7 kV 


5 80 plus 10 

perkV 
over 50 kV 


3. Surface of support arms 


75 2 


75 2 


75 6,8 


75 plus 5 

perkV 

over 8.7 kV 6 ' 8 - 10 


280 plus 5 

perkV 
over 50 kV 


4. Surface of structures: 












a. On jointly used structures 




125 2 . 


125 3,6,8 


125 plus 5 

per kV 

over 8.7 kV 6 ' 8 - 10 


330 plus 5 

perkV 
over 50 kV 


b. All other 


75 2 




75 6,8 


75 plus 5 

perkV 

over 8.7 kV 6, 8 - 10 


280 plus 5 

perkV 
over 50 kV 



I 



For guy wires, if practical. For clearances between span wires and communication conductors, see 
Rule 238C. 

On jointly used structures, guys that pass within 300 mm of supply conductors, and also pass within 
300 mm of communication cables, shall be protected with a suitable insulating covering where the guy 
passes the supply conductors, unless the guy is effectively grounded or insulated with a strain insulator 
at a point below the lowest supply conductor and above the highest communication cable. 

The clearance from an insulated or effectively grounded guy to a communication cable may be 
reduced to 75 mm when abrasion protection is provided on the guy or communication cable. 

135 
Copyright © 2001 IEEE. All rights reserved. 



T-235-6(m) PART 2. SAFETY RULES FOR OVERHEAD LINES T-235-6(m) 



z Communication conductors may be attached to supports on the sides or bottom of crossarms or 
surfaces of poles with less clearance. 

J This clearance applies only to supply conductors at the support below communication conductors, on 
jointly used structures. 

Where supply conductors are above communication conductors, this clearance may be reduced to 75 
mm. 

4 All clearances for line over 50 kV shall be based on the maximum operating voltage. For voltages 
exceeding 814 kV, the clearance shall be determined by the alternate method given by Rule 235E3. 

-> For supply circuits of to 750 V, this clearance may be reduced to 75 mm. 

" A neutral conductor meeting Rule 230E1 may be attached directly to the structure surface. 

' Guys and messengers may be attached to the same strain plates or to the same through bolts. 

° For open supply circuits of to 750 V and supply cables of all voltages meeting Rule 230C1, 2, or 3, 
this clearance may be reduced to 25 mm. No clearance is specified for phase conductors of such cables 
where they are physically restrained by a suitable bracket from abrasion against the pole. 

" The additional clearance for voltages in excess of 50 kV specified in Table 235-6 shall be increased 
3% for each 300 m in excess of 1000 m above mean sea level. 

10 Where the circuit is effectively grounded and the neutral conductor meets Rule 230E1, phase-to- 
neutral voltage shall be used to determine the clearance from the surface of support arms and structures. 

11 These clearances may be reduced by not more than 25% to a guy insulator, provided that full 
clearance is maintained to its metallic end fittings and the guy wires. The clearance to an insulated 
section of a guy between two insulators may be reduced by not more than 25% provided that full 
clearance is maintained to the uninsulated portion of the guy. 

12 Phase-to-phase voltages shall be determined according to Rule 235A3. 

13 These clearances apply to communication antennas operated at a radio frequency of to 750 V. 
Also see Rules 23514 and Rule 239. 



136 

Copyright © 2001 IEEE. All rights reserved. 



T-235-6(ft) 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-235-6(ft) 



ft 



Table 235-6 

Clearance in Any Direction From Line Conductors to Supports and to 

Vertical or Lateral Conductors, Span, or Guy Wires Attached to the Same Support 

[See also Rule 235E1, 235E3b(2), and 2351.] 



Clearance of line 
conductors from 


Communication lines 


Supply lines 
Circuit phase-to-phase voltage 


In general 
(in) 


On jointly 

used 
structures 

(in) 


Oto 
8.7 kV 

(in) 


Over 8.7 

to SO kV 

(in) 


Over 50 

to814kV 4 ' 9 

(in) 


1. Vertical and lateral conductors: 












a. Of the same circuit 


3 


3 


3 


3 plus 0.25 

perkV 
over 8.7 kV 


no value 
specified 


b. Of other circuits 12 ' 13 


3 


3 


6 5 


6 plus 0.4 

perkV 
over 8.7 kV 


23 plus 0.4 

perkV 
over 50 kV 


2. Span or guy wires, 11 or 
messengers attached to same 
structure: 












a. When parallel to line 


3 7 


6 1 - 7 


12 1 


12 plus 0.4 

per kV 
over 8.7 kV 


29 plus 0.4 

per kV 
over 50 kV 


b. Anchor guys 


3 7 


6 1 - 7 


6 1 


6 plus 0.25 
perkV 

over 8.7 kV 


16 plus 0.25 

perkV 
over 50 kV 


c. All other 


3 7 


6 1 - 7 


6 


6 plus 0.4 

perkV 
over 8.7 kV 


23 plus 0.4 

perkV 
over 50 kV 


3. Surface of support arms 


3 2 


3 2 


3 6,8 


3 plus 0.2 

perkV 

over 8.7 kV 6 ' 8 ' 10 


11 plus 0.2 

perkV 
over 50 kV 


4. Surface of structures: 

a. On jointly used structures 


— 


5 2 


5 3,6,8 


5 plus 0.2 

per kV 

over 8.7 kV 6 ' 8 ' 10 


13 plus 0.2 

perkV 
over 50 kV 


b. All other 


3 2 


— 


36,8 


3 plus 0.2 

per kV 

over 8.7 kV 6, 8 - 10 


11 plus 0.2 

perkV 
over 50 kV 






1 For guy wires, if practical. For clearances between span wires and communication conductors, see 
Rule 238C. 

On jointly used structures, guys that pass within 12 in of supply conductors, and also pass within 12 in of 
communication cables, shall be protected with a suitable insulating covering where the guy passes the supply 
conductors, unless the guy is effectively grounded or insulated with a strain insulator at a point below the lowest 
supply conductor and above the highest communication cable. 

The clearance from an insulated or effectively grounded guy to a communication cable may be reduced to 
3 in when abrasion protection is provided on the guy or communication cable. 

2 Communication conductors may be attached to supports on the sides or bottom of crossarms or surfaces 
of poles with less clearance. 

3 This clearance applies only to supply conductors at the support below communication conductors, on 
jointly used structures. 

Where supply conductors are above communication conductors, this clearance may be reduced to 3 in. 

4 All clearances for line over 50 kV shall be based on the maximum operating voltage. For voltages ex- 
ceeding 814 kV, the clearance shall be determined by the alternate method given by Rule 235E3. 

^ For supply circuits of to 750 V, this clearance may be reduced to 3 in. 

137 
Copyright © 2001 IEEE. All rights reserved. 



T-235-6(ft) PART 2. SAFETY RULES FOR OVERHEAD LINES 235E3A 



" A neutral conductor meeting Rule 230E1 may be attached directly to the structure surface. 

' Guys and messengers may be attached to the same strain plates or to the same through bolts. 

° For open supply circuits of to 750 V and supply cables of all voltages meeting Rule 230C1 , 2 or 3, this 
clearance may be reduced to 1 in. No clearance is specified for phase conductors of such cables where they 
are physically restrained by a suitable bracket from abrasion against the pole. 

^ The additional clearance for voltages in excess of 50 kV specified in Table 235-6 shall be increased 3% 
for each 1000 ft in excess of 3300 ft above mean sea level. 

*° Where the circuit is effectively grounded and the neutral conductor meets Rule 230E1, phase-to-neutral 
voltage shall be used to determine the clearance from the surface of support arms and structures. 

These clearances may be reduced by not more than 25% to a guy insulator, provided that full clearance 
is maintained to its metallic end fittings and the guy wires. The clearance to an insulated section of a guy be- 
tween two insulators may be reduced by not more than 25% provided that full clearance is maintained to the 
uninsulated portion of the guy. 

1^ Phase-to-phase voltages shall be determined according to Rule 235 A3. 

1:5 These clearances apply to communication antennas operated at a radio frequency of to 750 V. Also 
see Rules 23514 and Rule 239. 



E. Clearances in Any Direction From Line Conductors to Supports, and to Vertical or Lateral 
Conductors, Span, or Guy Wires Attached to the Same Support 

1. Fixed Supports 

Clearances shall be not less than those given in Table 235-6. 

EXCEPTION: For voltages exceeding 98 kV ac to ground or 139 kV dc to ground, clearances less than those 

required by Table 235-6 are permitted for systems with known switching-surge factor. (See Rule 235E3.) 

2. Suspension Insulators 

Where suspension insulators are used and are not restrained from movement, the clearance shall be in- 
creased so that the string of insulators may swing transversely throughout a range of insulator swing up 
to its maximum design swing angle without reducing the values given in Rule 235E1. The maximum 
design swing angle shall be based on a 290 Pa (6 lb/ft 2 ) wind on the conductor at final sag at 15 °C 
(60 °F). This may be reduced to a 190 Pa (4 lb/ft 2 ) wind in areas sheltered by buildings, terrain, or other 
obstacles. The displacement of the wires, conductors, and cables shall include deflection of flexible 
structures and fittings, where such deflection would reduce the clearance. 

3. Alternate Clearances for Voltages Exceeding 98 kV AC to Ground or 139 kV DC to Ground 
The clearances specified in Rules 235E1 and 235E2 may be reduced for circuits with known 
switching-surge factors but shall not be less than the following: 

a. Alternate Clearances to Anchor Guys, Surge-Protection Wires, and Vertical or Lateral 
Conductors 

The alternate clearances shall be not less than the crossing clearances required by Rule 233B2 
and Rules 233C3a and 233C3b for the conductor voltages concerned. For the purpose of this 
rule, anchor guys and surge-protection wires shall be assumed to be at ground potential. The 
limits of Rule 235E3b(2) shall apply to the clearance derived from Rules 233C3a and 233C3b. 



138 
Copyright © 2001 IEEE. All rights reserved. 



235E3b PART 2. SAFETY RULES FOR OVERHEAD LINES 235F5 



b. Alternate Clearance to Surface of Support Arms and Structures 

(1) Alternate Clearance 

(a) Basic Computation 

The alternate clearances shall be maintained under the expected loading conditions and 
shall be not less than the electrical clearances computed from the following equation. 
For convenience, clearances for typical system voltages are shown in Table 235-7. 



D = 1.00 

D = 39.37 
where 



V ■ {PU) ■ a] 1 - 667 , , , 

500* J b (m) 

V ■ (PU) ■ g-\ l -667 



500K 



b (in) 



V = maximum ac crest operating voltage to ground or maximum dc operating 
voltage to ground in kilovolts, 
PU = maximum switching-surge factor expressed in per-unit peak voltage to 
ground and defined as a switching-surge level for circuit breakers corre- 
sponding to 98% probability that the maximum switching surge generated 
per breaker operation does not exceed this surge level, or the maximum 
anticipated switching-surge level generated by other means, whichever is 
greater, 

a = 1.15, the allowance for three standard deviations with fixed insulator 

supports; 
= 1.05, the allowance for one standard deviation with free-swinging 

manipulators, 
b = 1.03, the allowance for nonstandard atmospheric conditions, 
K = 1.2, the configuration factor for conductor-to-tower window. 

(b) Atmospheric Correction 

The value of D shall be increased 3% for each 300 m (1000 ft) in excess of 450 m (1500 ft) 

above mean sea level. 
(2) Limits 

The alternate clearance shall not be less than the clearance of Table 235-6 for 169 kV ac. The al- 
ternate clearance shall be checked for adequacy of clearance to workers and increased, if neces- 
sary, where work is to be done on the structure while the circuit is energized. (Also see Part 4.) 

F. Clearances Between Circuits of Different Voltage Classifications Located in the Supply Space on the 
Same Support Arm 

Circuits of any one voltage classification as given in Table 235-5 may be maintained in the supply 
space on the same support arm with supply circuits of the next consecutive voltage classification only 
under one or more of the following conditions: 

1 . If they occupy positions on opposite sides of the structure. 

2. If in bridge-arm or sidearm construction, the clearance is not less than the climbing space required 
for the higher voltage concerned and provided for in Rule 236. 

3. If the higher-voltage conductors occupy the outer positions and the lower- voltage conductors oc- 
cupy the inner positions. 

4. If series lighting or similar supply circuits are ordinarily dead during periods of work on or above 
the support arm concerned. 

5. If the two circuits concerned are communication circuits (located in the supply space in accor- 
dance with Rule 224A), or one circuit is such a communication circuit and the other is a supply 
circuit of less than 8.7 kV, and both are owned by the same utility, provided they are installed as 
specified in Rule 235F1 or 235F2. 



139 
Copyright © 2001 IEEE. All rights reserved. 



I 



T-235-7 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



235G3 



Table 235-7 
Clearance in Any Direction From Line Conductors to Supports 

(See also Rule 235E3b and 235E3b(l)(a).) 



Maximum 

operating 

voltage phase 

to phase 

(kV) 


Switching- 
surge factor 
(per unit) 


Switching 
surge 

(kV) 


Computed clearance to supports 


Fixed 


Free swinging at 
maximum angle 


(m) 


(ini 


(m) 


(iii> 


242 


2.4 


474 


0.89 


35 < 


0.89 


35' 




2.6 


514 


1.00 


40 


0.89 


35 




2.8 


553 


1.14 


45 
50 2 
50- 
35 ' 


0.97 


■ 1X 




3.0 


593 


1.27 


1.10 


41 




3.2 


632 


1.27 


1.10 


362 


1.6 


473 


0.89 


0.89 


35 ' 




1.8 


532 


1.07 


42 


0.89 


.. 




2.0 


591 


1.27 


50 


1.20 




2.2 


650 


1.50 


59 


1.20 


51 




2.4 


709 


1.73 


68 


1.20 


59 




2.5 


739 


1.85 


73 2 
70 


1.20 


63 


550 


1.6 


719 


1.80 


1.50 


60 




1.8 


808 


2.15 


X5 


1.85 


73 




2.0 


898 


2.60 


10 1 


2.20 


87 




2.2 


988 


2.80 


111- 1 
no 

158 


2.20 


101 

111 


800 


1.6 


1045 


3.3 


2.80 




1.8 


1176 


4.0 


2.80 


135 




1.9 


1241 


4.1 


161- 
161- 


3.8 


148 




2.0 


1306 


4.1 


4.1 


161 : 



T 



Limited by Rule 235E3(b)(2) 



2 Need not be greater than specified in Rules 235E1 and 235E2. 



G. Conductor Spacing: Vertical Racks 

Conductors or cables may be carried on vertical racks or separate brackets other than wood placed 
vertically on one side of the structure and securely attached thereto with less clearance between the 
wires, conductors, or cables than specified in Rule 235C if all the following conditions are met: 

1. The voltage shall not be more than 750 V, except supply cables and conductors meeting Rules 
230C1 or 230C2, which may carry any voltage. 

2. Conductors shall be of the same material or materials, except that different materials may be used 
if their sag tension characteristics and arrangement are such that the spacing specified in Rule 
235G3 is maintained under all service conditions. 

3. Vertical spacing between conductors shall be not less than the following: 

140 
Copyright © 2001 IEEE. All rights reserved. 



235H 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



236C 



Span length 


Vertical spacing between conductors 


(m) \ (ft) 


(mm) 


(in) 


0to45 1 to 150 


100 


■ ■■■."■:'■ 4 '-■■ ':'■: ' ■ 


45 to 60 


IN) TO J' Kl 


150 


6 

.: : :. , -8 '■.:■;■ 


60 to 75 


:oot...:.5o 


200 


75 to 90 


250 to 300 


300 | . : : : - ■ ..12 ■. . ; .:.-. 



EXCEPTION: The vertical spacing may be reduced where the conductors are held apart by in- 
termediate spacers, but may not be less than 100 mm (4 in). 



H. Clearance and Spacing Between Communication Conductors, Cables, and Equipment 

1. The spacing between messengers supporting communication cables should be not less than 
300 mm (12 in) except by agreement between the parties involved. 

2. The clearances between the conductors, cables, and equipment of one communiation utility to 
those of another, anywhere in the span, shall be not less than 100 mm (4 in), except by agreement 
between the parties involved. 

I. Clearances in Any Direction From Supply Line Conductors to Communication Antennas in the 
Supply Space Attached to the Same Supporting Structure 

1. General 

Communication antennas located in the supply space shall be installed and maintained only by 
personnel authorized and qualified to work in the supply space in accordance with the applicable 
rules of Sections 42 and 44. See also Rule 224A. 

2. Communication Antenna 

The clearance between a communication antenna operated at a radio frequency of to 750 V and 
a supply line conductor shall be not less than the value given in Table 235-6, row lb. 
NOTE: The antenna functions as a rigid, vertical or lateral open wire communication conductor. 

3. Equipment Case That Supports a Communication Antenna 

The clearance between an equipment case that supports a communication antenna and a supply 
line conductor shall be not less than the value given in Table 235-6, Row 4a. 

4. Vertical or Lateral Communication Conductors and Cables Attached to a Communication 
Antenna 

The clearance between a supply line conductor and the vertical or lateral communciation conduc- 
tor and cable attached to a communication antenna shall be not less than the value given in 
Rule 239. 

236. Climbing Space 

The following requirements apply only to portions of structures that workers ascend. 
A. Location and Dimensions 

1 . A climbing space having the horizontal dimensions specified in Rule 236E shall be provided past 
any conductors, support arms, or other parts. 

2. The climbing space need be provided on one side or corner of the support only. 

3. The climbing space shall extend vertically past any conductor or other part between levels above 
and below the conductor as specified in Rules 236E, F, G, and I, but may otherwise be shifted from 
any side or comer of the support to any other side or corner. 



i 



B. 



Portions of Supporting Structures in Climbing Space 

Portions of the supporting structure, when included in one side or corner of the climbing space, are 

not considered to obstruct the climbing space. 



C. Support Arm Location Relative to Climbing Space 

RECOMMENDATION: Support arms should be located on the same side of the pole. 

EXCEPTION: This recommendation does not apply where double crossarms are used on any pole or where cros- 

sarms on any pole are not all parallel. 

141 
Copyright © 2001 IEEE. All rights reserved. 



236D PART 2. SAFETY RULES FOR OVERHEAD LINES 236E 



D. Location of Equipment Relative to Climbing Space 

1. All supply and communication equipment such as transformers, regulators, capacitors, cable 

terminals (potheads), amplifiers, loading coils, surge arresters, switches, etc., when located below 

conductors or other attachments, shall be mounted outside of the climbing space. 
2. All exposed ungrounded conductive parts of luminaires and their supports that are not insulated 

from current-carrying parts shall be maintained at not less than 500 mm (20 in) from the surface 

of their supporting structure. 

EXCEPTION 1: This may be reduced to 125 mm (5 in) if located on the side of the structure opposite the 

designated climbing space. 

EXCEPTION 2: This does not apply where the equipment is located at the top or other vertical portion of the 

structure that is not subject to climbing. 

E. Climbing Space Between Conductors 

Climbing space between conductors shall be not less than the horizontal dimensions specified in 
Table 236-1. These dimensions are intended to provide a clear climbing space of 600 mm (24 in) 
while the conductors bounding the climbing space are covered with temporarily installed protective 
covering rated for the voltage involved. The climbing space shall be provided both along and across 
the line and shall be projected vertically not less than 1.0 m (40 in) above and below the limiting con- 
ductors. Where communication conductors are above supply conductors of more than 8.7 kV to 
ground or 15 kV line to line, the climbing space shall be projected vertically at least 1.50 m (60 in) 
above the highest supply conductors. 

EXCEPTION 1: This rule does not apply if it is the unvarying practice of the employers concerned to prohibit 
employees from ascending beyond the conductors or equipment of a given line or structure unless the conductors 
or equipment are de-energized and grounded per Rule 444D. 

EXCEPTION 2: For supply conductors carried on a structure in a position below communications facilities in the man- 
ner permitted in Rule 220B2, the climbing space need not extend more than 600 mm (2 ft) above such supply space. 
EXCEPTION 3: If the conductors are owned, operated, or maintained by the same utility, the climbing space may 
be provided by temporarily moving the line conductors using live-line tools. 



142 
Copyright © 2001 IEEE. All rights reserved. 



T-236-1 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-236-1 



Table 236-1 
Horizontal Clearance Between Conductors Bounding the Climbing Space 

(All voltages are between the two conductors bounding the climbing space except for communication 

conductors, which are voltage to ground. Where the two conductors are in different circuits, the voltage between 

conductors shall be the arithmetic sum of the voltages of each conductor to ground for a grounded circuit, or 

phase to phase for an ungrounded conductor. See also Rule 236E.) 



Character of 

conductors 

adjacent to 

climbing space 


Voltage of 
conductors 


■a 

Horizontal clearance between conductors bounding the climbing space 


On structures used solely by 


On jointly used structures 


Communication 
conductors 


Supply 
conductors 


Supply 

conductors 

above 

communication 

conductors 


Communication 

conductors above 

supply conductors 1 


(m) 


(in! 


(m) 


(in. 


(m) 


(ill! 


(m) 


x ;: : -(in) : x':':" 


1 . Communication 
conductors 


to 150 V 


0.60 


■ . no : . . 

lV(.]li:iC!lKTlts 




— 




(lKJ[i;2). 


0.60 


no 
requirements 

: :: . ;.24 : : ''- 

lecoiruriemled 


exceeding 
150 V 


24 
recommended 




— 




(hotc2) 


2. Supply cables 
meeting Rule 
230C1 


all voltages 












(note 2) 




■ ■■■■■; no'. ■'.■■. 
requirements 


3. Supply cables 
meeting Rule 
230C2or3 


all voltages 


— 


— 


0.60 


' : -:24-:": 


0.60 


24 


0.75 


■ ','■ ;'30.- : - ■ 
30 


4. Open supply 
line 

conductors 
and supply 
cables 

meeting Rule 
230D 


to 750 V 


— 


-- 


0.60 


24 


0.60 


24 


0.75 


750 V to 
15 kV 


— 


— 


0.75 


30 


0.75 


-u 


0.75 


■ ::"30.' ■:■; 
'.:'■.■:;. 36- ;■'.;■; 


15 kV to 
28 kV 


— . : ' ■ — ''■ ■ 


0.90 


36 


0.90 


?6 


0.90 


28 kV to 
38 kV 


— 


1.00 


40 


1.00 


40 






38 kV to 
50 kV 


— ■:■: : : — :'. '': 


1.17 


46 


1.17 


46 




■ ■ ' " ■ : ■ ' ■ ■ 


50 kV to 
73 kV 


— | ..;.— ; : : : ' : . 


1.40 I .-4 


1.40 


54 






exceeding 
73 kV 


_ 


>1.40 









I 



1 This relation of levels in general is not desirable and should be avoided. 

2 Climbing space shall be the same as required for the supply conductors immediately above, with a 
maximum of 0.75 m (30 in) except that a climbing space of 0.41 m (16 in) across the line may be employed 
for communication cables or conductors where the only supply conductors at a higher level are secondaries 
(0 to 750 V) supplying airport or airway marker lights or crossing over the communication line and attached 
to the pole top or to a pole-top extension fixture. 

3 Attention is called to the operating requirements of Rules 441 A and 446C, Part 4, of this code. 



143 
Copyright © 2001 IEEE. All rights reserved. 



236F PART 2. SAFETY RULES FOR OVERHEAD LINES 2361 



F. Climbing Space on Buckarm Construction 

Method of Providing Climbing Space on Buckarm Construction 

The full width of climbing space shall be maintained on buckarm construction and shall extend ver- 
tically in the same position at least 1.0 m (40 in) [or 1.50 m (60 in) where required by Rule 236E] 
above and below any limiting conductor. 

A six-pin crossarm having pin spacing of 370 mm (14.5 in) may be used to provide a 750 mm 
(30 in) climbing space on one corner of a junction pole by omitting the pole pins on all arms, and 
inserting pins midway between the remaining pins so as to give a spacing of 185 mm (7.25 in), pro- 
vided that all of the following conditions are met: 

(1) Circuits are less than 8.7 kV to ground or 15 kV line to line 

(2) Span lengths do not exceed 45 m (150 ft) 

(3) Sags do not exceed 380 mm (15 in) for wires of AWG No. 2 and larger sizes, or 750 mm 
(30 in) for wires smaller than AWG No. 2 

(4) Each conductor on the end of every arm is tied to the same side of its insulator 

(5) The spacing on the next pole is not less than 370 mm (14.5 in) 

G. Climbing Space Past Longitudinal Runs Not on Support Arms 

The full width of climbing space shall be provided past longitudinal runs and shall extend vertically 
in the same position from 1 .0 m (40 in) below the run to a point 1 .0 m (40 in) above [or 1 .50 m (60 in) 
where required by Rule 236E]. The width of climbing space shall be measured from the longitudinal 
run concerned. Longitudinal runs on racks, or cables on messengers, are not considered as obstructing 
the climbing space if all wires concerned are covered by rubber protective equipment or otherwise 
guarded as an unvarying practice before workers climb past them. This does not apply where com- 
munication conductors are above the longitudinal runs concerned. 

EXCEPTION 1: If a supply longitudinal run is placed on the side or corner of the supporting structure where 
climbing space is provided, the width of climbing space shall be measured horizontally from the center of the 
structure to the nearest supply conductors on support arms, under both of the following conditions: 

(1) Where the longitudinal run consists of open supply conductors carrying not more than 750 V, or supply ca- 
bles and conductors meeting Rule 230C, all voltages; and is supported close to the structure as by brackets, racks, 
or pins close to the structure. 

(2) Where the nearest supply conductors on support arms are parallel to and on the same side of the structure as 
the longitudinal run and within 1.20 m (4 ft) above or below the run. 

EXCEPTION 2: For supply conductors carried on a structure in a position below communications facilities in 
the manner permitted in Rule 220B2, the climbing space need not extend more than 600 mm (2 ft) above such 
supply space. 

EXCEPTION 3: A service drop less than 750 V and meeting Rule 230C is not considered to obstruct the climbing 
space if all conductors concerned are covered by rubber protective equipment or otherwise guarded as an 
unvarying practice before workers climb past them, provided that such a service drop is (1) not closer to the 
longitudinal run at the point of attachment than the diameter of the pole plus 125 mm (5 in) measured 
horizontally, and (2) not closer than 950 mm (38 in) measured horizontally to the longitudinal run at a point 750 
mm (30 in) on the run measured from the point of attachment at the pole. See Fig 236-1. 

H. Climbing Space Past Vertical Conductors 

Vertical runs physically protected by suitable conduit or other protective covering and securely at- 
tached without spacers to the surface of the line structure are not considered to obstruct the climbing 
space. 

I. Climbing Space Near Ridge-Pin Conductors 

The climbing space specified in Table 236-1 shall be provided above the top support arm to the ridge- 
pin conductor but need not be carried past it. 

144 
Copyright © 2001 IEEE. All rights reserved. 



F-236-1 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



237B3 



750 mm 
(30 in) 



POLE DIAMETER 
PLUS 125 mm (5 in) 




SERVICE DROP 



G_ OF LONGITUDINAL RUN 



LEGEND 



BOUNDARY OF CLIMBING SPACE 



Fig 236-1 
Rule 236G, Exception 3 



I 



237. Working Space 

A. Location of Working Spaces 

Working spaces shall be provided on the climbing face of the structure at each side of the climbing 
space. 

B. Dimensions of Working Spaces 

1. Along the Support Arm 

The working space shall extend from the climbing space to the outmost conductor position on the 
support arm. 

2. At Right Angles to the Support Arm 

The working space shall have the same dimension as the climbing space (see Rule 236E). This di- 
mension shall be measured horizontally from the face of the support arm. 

3. Vertically 

The working space shall have a height not less than that required by Rule 235 for the vertical sep- 
aration of line conductors carried at different levels on the same support. 



145 
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237C 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



237F 



C. Location of Vertical and Lateral Conductors Relative to Working Spaces 

The working spaces shall not be obstructed by vertical or lateral conductors. Such conductors shall be 
located on the opposite side of the pole from the climbing side or on the climbing side of the pole at 
a distance from the support arm at least as great as the width of climbing space required for the highest 
voltage conductors concerned. Vertical conductors enclosed in suitable conduit may be attached on 
the climbing side of the structure. 

D. Location of Buckarms Relative to Working Spaces 

Buckarms may be used under any of the following conditions, provided the climbing space is main- 
tained. Climbing space may be obtained as in Rule 236F. 
1 . Standard Height of Working Space 

Lateral working space of the height required by Table 235-5 shall be provided between the 
crossing or tap line conductors attached to the buckarm and the main line conductors. This may 
be accomplished by increasing the spacing between the line support arms, as shown in Fig 237-1. 




^v*** 



CLEARANCE AS 
REQUIRED IN 
RULE 235E1 



Fig 237-1 
Obstruction of Working Space by Buckarm 

2. Reduced Height of Working Space 

Where no circuits exceeding 8.7 kV to ground or 15 kV line to line are involved and the clearances 
of Rules 235Bla and 235Blb are maintained, conductors supported on buckarms may be placed 
between line conductors having normal vertical spacing, even though such buckarms obstruct the 
normal working space, provided that a working space of not less than 450 mm (18 in) in height is 
maintained either above or below line conductors and buckarm conductors. 

EXCEPTION: The above working space may be reduced to 300 mm (12 in) if both of the following condi- 
tions exist: 

(a) Not more than two sets of the line arms and buckarms are involved. 

(b) Working conditions are rendered safe by providing rubber protective equipment or other suit- 
able devices to insulate and cover line conductors and equipment that are not being worked 
upon. 



E. Guarding of Energized Equipment 

Exposed energized parts of equipment such as switches, circuit breakers, surge arresters, etc., shall be 
enclosed or guarded if all of the following conditions apply: 

1. The equipment is located below the top conductor support. 

2. The equipment is located on the climbing side of the structure. 

3. The requirements of Rule 441 , Part 4, of this code cannot be met. 

F. Working Clearances From Energized Equipment 

All parts of equipment such as switches, fuses, transformers, surge arresters, luminaires and their sup- 
port brackets, etc., or other connections that may require operation or adjustment while energized and 

146 
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238 PART 2. SAFETY RULES FOR OVERHEAD LINES 238E 



exposed at such times, shall be so arranged with respect to each other, other equipment, vertical and 
lateral conductors, and portions of the supporting structure, including supporting platforms or struc- 
tural members, that in adjustment or operation no portion of the body, including the hands, need be 
brought closer to any exposed energized parts or conductors than permitted in Part 4, Rules 441 or 
446 of this code. 

238. Vertical Clearance Between Certain Communications and Supply Facilities Located 
on the Same Structure 

A. Equipment 

For the purpose of measuring clearances under this rule, equipment shall be taken to mean non-cur- 
rent-carrying metal parts of equipment, including metal supports for cables or conductors, and metal 
support braces that are attached to metal supports or are less than 25 mm (1 in) from transformer cases 
or hangers that are not effectively grounded. 

B. Clearances in General 

Vertical clearances between supply conductors and communications equipment, between communi- 
cation conductors and supply equipment, and between supply and communications equipment shall 
be as specified in Table 238-1, except as provided in Rule 238C. 

C. Clearances for Span Wires or Brackets 

Span wires or brackets carrying luminaires, traffic signals, or trolley conductors shall have at least the 
vertical clearances in millimeters or inches from communications equipment set forth in Table 238-2. 

D. Clearance of Drip Loops of Luminaire or Traffic Signal Brackets 

If a drip loop of conductors entering a luminaire bracket or traffic signal bracket from the surface of 
the structure is above a communication cable, the lowest point of the loop shall be at least 300 mm 
(12 in) above communication cable or through bolt. 

EXCEPTION: The above clearance may be reduced to 75 mm (3 in) if the loop is covered by a suitable nonme- 
tallic covering that extends at least 50 mm (2 in) beyond the loop. 

E. Communication Worker Safety Zone 

The clearance specifications of Rules 235C and 238 create a communication worker safety zone be- 
tween the facilities located in the supply space and facilities located in the communication space, both 
at the structure and in the span between structures. Except as allowed by Rules 238C, 238D, and 239, 
no supply or communication facility shall be located in the communication worker safety zone. 



I 



147 
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T-238-1 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-238-2 



Table 238-1 

Vertical Clearance Between Supply Conductors and Communications Equipment, 

Between Communication Conductors and Supply Equipment, 

and Between Supply and Communications Equipment 

(Voltages are phase to ground for effectively grounded circuits and those other circuits where all ground 

faults are cleared by promptly de-energizing the faulted section, both initially and following subsequent 

breaker operations. See the definitions section for voltages of other systems. See also Rule 238B.) 



Supply voltage 

(kV) 


Vertical clearance 


(m) 


.; :■:';:■/'. :(»n) : : : ..X "'-■■. 


1 . Grounded conductor and messenger 
hardware and supports 


0.75 


■ '■■ ■:■.': : ■■■■''^Q-O; .''■''■■ : '' 

■■'. ' :'■";:.■ ■ :40 1: : ..'■. '■■'■':■ 

40 plus 0.4 per kV ' 
over S.7 kV 


2. to 8.7 


1.00 


3. Over 8.7 


1.00 plus 0.01 per kV 
over 8.7 kV 



1 Where non-current-carrying parts of supply equipment are effectively grounded and the associated neutral 
meeting Rule 230E1 or supply cables meeting Rule 230C1 (including the support brackets) are bonded to 
communication messengers at intervals meeting Rule 92C through out well-defined areas and where commu- 
nication is at lower levels, clearances may be reduced to 0.75 m (30 in). 

Table 238-2 
Vertical Clearance of Span Wires and Brackets From Communication Lines 

(See also Rule 238C.) 





Carrying luminaires or traffic 
signals 


Carrying trolley conductors 


Not effectively 
grounded 


Effectively 
grounded 


Not effectively 
grounded 


Effectively 
grounded 


(mm) 1 -;-(in)-.-: 


(mm i i ii 


(mm) 


(in) 


(mm) (in) 


Above communication 
support arms 


500 


20 ! 


500 


500 


2(1 


500 


20 ' 


Below communication 
support arms 


1000 


40 > 
20 ' 

40 4 
20' 
If, 1 


600 .24 




600 


24 


600 


24 


Above messengers carrying 
communication cables 


500 


100 


■ 

4 


300 


12 


100 I 4 


Below messengers carrying 
communication cables 


1000 


100 


300 


12 


100 


' 4: : ; 


From terminal box of 
communication cable 


500 


100 


; 4 


300 


n 2 


100 


:'.-..■ 4.' .". 


From communication brackets, 
bridle wire rings, or drive hooks 


410 


100 | . 1 


100 


4 


100 


■ ■■'4'-'- ■■ 



This may be reduced to 300 mm (12 in) for either span wires or metal parts of brackets at points 1.0 m 
(40 in) or more from the structure surface. 

2 Where it is not practical to obtain a clearance of 300 mm (1 ft) from terminal boxes of communication 
cables, all metal parts of terminals shall have the greatest possible separation from fixtures or span wires in- 
cluding all supporting screws and bolts of both attachments. 

This may be reduced to 600 mm (24 in) for luminaires and traffic signals operating at less than 150 V to 
ground. 

4 This may be reduced to 500 mm (20 in) for luminaires and traffic signals operating at less than 150 V to 
ground. 



148 
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239 PART 2. SAFETY RULES FOR OVERHEAD LINES 239E2 



239. Clearance of Vertical and Lateral Facilities From Other Facilities and Surfaces on the 
Same Supporting Structure 

Vertical and lateral conductors shall have the clearances and separations required by this rule from 
other facilities or surfaces on the same supporting structure. 

A. General 

1. Grounding conductors, surge-protection wires, neutral conductors meeting Rule 230E1, insulated 
communication conductors and cables, supply cables meeting Rule 230C1, insulated supply 
cables of to 750 V, or conduits may be placed directly on the supporting structure. These 
conductors, wires, cables, and conduits shall be securely attached to the surface of the structure. 
Cables not in conduit shall be installed in such a manner as to avoid abrasion at the point of 
attachment. 

2. Supply circuits of the same or next voltage classification may be placed in the same duct, if each 
circuit or set of wires is enclosed in a metal sheath. 

3. Paired communication conductors in rings may be attached directly to a structure or messenger. 

4. Insulated supply circuits of 600 V or less and not exceeding 5000 W may be placed in the same 
cable with control circuits with which they are associated. 

5. The term nonmetallic covering as used in Rule 239 refers to material other than a cable jacket that 
provides an additional barrier against physical contact. 

6. Where guarding and protection are required by other rules, either conduit or U-guards may be 
used. A backing plate shall be used with a U-guard unless the U-guard fits tightly to the supporting 
structure surface. 

B. Location of Vertical or Lateral Conductors Relative to Climbing Spaces, Working Spaces, and Pole 
Steps 

Vertical or lateral conductors shall be located so that they do not obstruct climbing spaces, or lateral 
working spaces between line conductors at different levels, or interfere with the safe use of pole steps. 
EXCEPTION: This rule does not apply to portions of the structure that workers do not ascend while the conduc- 
tors in question are energized. 
NOTE: See Rule 236H for vertical runs in conduit or other protective covering. 

C. Conductors Not in Conduit 

Conductors not encased in conduit shall have the same clearances from conduits as from other 
surfaces of structures. 

D. Guarding and Protection Near Ground 

1 . Where within 2.45 m (8 ft) of the ground, or other areas readily accessible to the public, all vertical 
conductors and cables shall be guarded. 

EXCEPTION: This guarding may be omitted from grounding conductors used to ground multi-grounded cir- 
cuits or equipment (communications or supply); communication cables or conductors; armored cables; or 
conductors used solely to protect structures from lightning. 

2. Where guarding is required, conductors and cables shall be protected by covering or conduit that 
gives suitable mechanical protection. 

3. When guarding is not required, conductors and cables shall be securely attached to the surface of 
the structure or to standoff brackets and located, where practical, on the portion of the structure 
having the least exposure to mechanical damage. 

4. Guards that completely enclose grounding conductors of lightning-protection equipment shall be 
of nonmetallic materials or shall be bonded at both ends to the grounding conductor. 

E. Requirements for Vertical and Lateral Supply Conductors on Supply Line Structures or Within 
Supply Space on Jointly Used Structures 

1. General Clearances 

In general, clearances shall be not less than the values specified in Table 239-1 or Rule 23 5E. 

2. Special Cases 

The following requirements apply only to portions of a structure that workers ascend while the 
conductors in question are energized. 

149 
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239E2a PART 2. SAFETY RULES FOR OVERHEAD LINES 239G1 



a. General 

| If open-line conductors are within 1 .20 m (4 ft) of the pole, vertical conductors shall be run in 

one of the following ways: 
( (1) The clearance between open vertical conductors and pole-surface shall be not less than 

that given in Table 239-2 within the zone specified in the table. 
(2) Within the zone above and below open supply conductors as given in Table 239-2, 
vertical and lateral conductors or cables attached to the surface of the structure shall be 
enclosed in nonmetallic conduit or protected by non-metallic covering. 
EXCEPTION: This conduit or covering may be omitted from grounding conductors, surge- 
protection wires, neutral conductors meeting Rule 230E1, supply cables meeting Rule 230C1, and 
jacketed multiple-conductor supply cables of to 750V, where such conductors or cable are not in 
the climbing space. 

For the purpose of this exception, a jacketed multiple-conductor cable is a cable with a jacket 
enclosing the entire cable assembly. 

b. Conductors to Luminaires 

On structures used only for supply lines or on jointly used structures where the luminaire 
bracket is 1.0 m (40 in) or more above all communication attachments, open wires may be run 
from the supply line arm direcdy to the head of a luminaire, provided the clearances of Table 
239- 1 are obtained and the open wires are securely supported at both ends. 

F. Requirements for Vertical and Lateral Communication Conductors on Communication Line 
Structures or Within the Communication Space on Jointly Used Structures 

1. Clearances From Communication Conductors 

The clearances of uninsulated vertical and lateral communication conductors from other commu- 
nication conductors (except those in the same ring run) and from guy, span, or messenger wires 
shall be not less than those given in Rule 235E1, Table 235-6. 

2. Clearances From Supply Conductors 

The vertical clearance of vertical and lateral insulated communication conductors shall be not less 
| than 1.0 m (40 in) from any supply conductors (other than vertical runs or luminaire leads) of 

8.7 kV or less, or 1 .0 m (40 in) plus 10 mm (0.4 in) per kV over 8.7 to 50 kV. The additional clear- 
ance of Rule 235C2 is applicable when the voltage exceeds 50 kV. 

EXCEPTION 1: May be reduced to 0.75 m (30 in) from supply neutrals meeting Rule 230E1, cables meeting 
Rule 230C1, and fiber optic-supply cables where the supply neutral or messenger is bonded to the commu- 
nication messenger. 

EXCEPTION 2: These clearances do not apply where the supply circuits involved are those carried in the 
manner specified in Rule 220B2. 

G. Requirements for Vertical Supply Conductors and Cables Passing Through Communication Space on 
Jointly Used Line Structures 

1 . Guarding — General 

Vertical supply conductors or cables attached to the structure shall be guarded with suitable con- 
duit or covering from 1.0 m (40 in) above the highest communication attachment to 1.80 m (6 ft) 
below the lowest communication attachment. 

EXCEPTION 1 : This conduit or covering may be omitted from neutral conductors meeting Rule 230E 1 , sup- 
ply cables meeting Rule 230C1, and jacketed multiple-conductor supply cables of to 750 V, where such 
conductors or cable are not in the climbing space. 

For the purpose of this exception, a jacketed multiple-conductor cable is a cable with a jacket enclosing 
the entire cable assembly. 

EXCEPTION 2: This conduit or covering may be omitted from supply grounding conductors where there are 
no trolley or ungrounded traffic signal attachments, or ungrounded street lighting fixtures located below the 
communication attachment, provided: 

(a) The grounding conductor is directly (metallically) connected to a conductor which forms part of an ef- 
fective grounding system, 

(b) The grounding conductor has no connection to supply equipment between the grounding electrode and 
the effectively grounded conductor unless the supply equipment has additional connections to the effec- 
tively grounded conductor, and 

(c) The grounding conductor is bonded to grounded communication facilities at that structure. 

150 
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239G2 PART 2. SAFETY RULES FOR OVERHEAD LINES 239H3 



2. Cables and Conductors in Conduit or Covering 

Cables and conductors of all voltages may be run in a nonmetallic conduit or covering or in a 
grounded metallic conduit or covering in accordance with Rule 239 A 1 . Where a metallic conduit 
or covering is not bonded to grounded communications facilities at that structure, such metal 
conduit or covering shall have a nonmetallic covering from 1.0 m (40 in) above the highest 
communication attachment to 1.80 m (6 ft) below the lowest communication attachment. 

3. Protection Near Trolley, Ungrounded Traffic Signal, or Ungrounded Luminaire Attachments 
Vertical supply conductors or cables attached to the structure shall be guarded with suitable 
nonmetallic conduit or covering on structures that carry a trolley or ungrounded traffic signal 
attachment or an ungrounded luminaire that is attached below the communication cable. The 
cable shall be protected with nonmetallic covering from 1.0 m (40 in) above the highest 
communication wire to 1 .80 m (6 ft) below the lowest trolley attachment or ungrounded luminaire 
fixture or ungrounded traffic signal attachment. 

4. Aerial Services 

Where supply cables are used as aerial services, the point where such cables leave the structure 
shall be at least 1.0 m (40 in) above the highest or 1.0 m (40 in) below the lowest communication 
attachment. Within the communication space, all splices and connections in the energized phase 
conductors shall be insulated. 

5. Clearance From Through Bolts and Other Metal Objects 

Vertical runs of supply conductors or cables shall have a clearance of not less than 50 mm (2 in) 
from exposed through bolts and other exposed metal objects attached thereto that are associated 
with communication line equipment. 

EXCEPTION: Vertical runs of effectively grounded supply conductors may have a clearance of 25 mm 
(1 in). 

H. Requirements for Vertical Communication Conductors Passing Through Supply Space on Jointly 
Used Structures 

All vertical runs of communication conductors passing through supply space shall be installed as 
follows: 

1 . Metal-Sheathed Communication Cables 

Vertical runs of metal-sheathed communication cables shall be covered with suitable nonmetallic 
material, where they pass trolley feeders or other supply line conductors. This nonmetallic cov- 
ering shall extend from a point 1.0 m (40 in) above the highest trolley feeders or other supply con- 
ductors, to a point 1.80 m (6 ft) below the lowest trolley feeders or other supply conductors, but 
need not extend below the top of any mechanical protection that may be provided near the ground. 
EXCEPTION 1: Communication cables may be run vertically on the pole through space occupied by railroad 
signal supply circuits in the lower position, as permitted in Rule 220B2, without covering within the supply 
space. 
EXCEPTION 2: Covering is not required in the supply space on metallic or concrete supporting structures. 

2. Communication Conductors 

Vertical runs of insulated communication conductors shall be covered with suitable nonmetallic 

material, to the extent required for metal-sheathed communication cables in Rule 239H1, where 

such conductors pass trolley feeders or supply conductors. 

EXCEPTION 1: Communication conductors may be run vertically on the structure through space occupied 

by railroad- signal supply circuits in the lower position, as permitted in Rule 220B2, without covering within 

the supply space. 

EXCEPTION 2: Covering is not required in the supply space on metallic or concrete supporting structures. 

3. Communication Grounding Conductors 

Vertical communication grounding conductors shall be covered with suitable nonmetallic mate- 
rial between points at least 1 .80 m (6 ft) below and 1 .0 m (40 in) above any trolley feeders or other 
supply line conductors by which they pass. 

EXCEPTION 1: Communication grounding conductors may be run vertically on the structure though space 
occupied by railroad-signal supply circuits in the lower position, as permitted in Rule 220B2, without cov- 
ering within the supply space. 
EXCEPTION 2: Covering is not required in the supply space on metallic or concrete supporting structures. 

151 
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I 



239H4 PART 2. SAFETY RULES FOR OVERHEAD LINES 239J2c 



4. Clearance From Through Bolts and Other Metal Objects 

Vertical runs of communication conductors or cables shall have a clearance of one-eighth of the 
pole circumference but not less than 50 mm (2 in) from exposed through bolts and other exposed 
metal objects attached thereto that are associated with supply line equipment. 
EXCEPTION: Vertical runs of effectively grounded communication cables may have a clearance of 25 mm 
(1 in). 

I. Operating Rods 

Effectively grounded or insulated operating rods of switches are permitted to pass through the com- 
munication space, but shall be located outside of the climbing space. 

J. Additional Rules for Standoff Brackets 

1. Standoff brackets may be used to support the conduit(s). Cable insulation appropriate for the in- 
tended service is required; non-metallic conduit shall not be used to meet basic insulation 
requirements. 

NOTE: See Rule 217A2. 

2. Standoff brackets may be used to support the following types of cable enclosed within a single 
outer jacket or sheath (cable only without conduit): 

a. Communication 

b. 230Cla supply (any voltage) 

c. Supply less than 750 V 
ATOTE:SeeRule217A2. 



152 
Copyright © 2001 IEEE. All rights reserved. 



T-239-l(m) 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-239-l(in) 



m 



Table 239-1 
Clearance of Open Vertical and Lateral Conductors 

(Circuit Phase-to-Phase Voltage. See also Rules 239E1 and 239E2b.) 



Clearance of open vertical and lateral 
conductors 


to 8.7 kV 
(mm) 


Over 8.7 to 50 kV 
(mm) 


Over 50 kV 4 
(mm) 


From surfaces of supports 


75 !- 2 


75 plus 5 per kV 
over 8.7 kV 


280 plus 5 per kV 
over 50 kV 


From span, guy, and messenger wires 


150 


150 plus 10 per kV 
over 8.7 kV 3 


580 plus 
10 per kV 
over 50 kV 3 



1 A neutral conductor meeting Rule 230E1 may be attached directly to the structure surface. 

2 For supply circuits of to 750 V, this clearance may be reduced to 25 mm. 

3 Multiplier may be reduced to 6.5 mm/kV for anchor guys. 

4 The additional clearance for voltages in excess of 50 kV specified in Table 239-1 shall be increased 
3% for each 300 m in excess of 1000 m above mean sea level. 

-* These clearances may be reduced by not more than 25% to a guy insulator, provided that full 
clearance is maintained to its metallic end fittings and the guy wires. The clearance to an insulated section 
of a guy between two insulators may be reduced by not more than 25% provided that full clearance is 
maintained to the uninsulated portion of the guy. 



in 



Table 239-1 
Clearance of Open Vertical and Lateral Conductors 

(Circuit Phase-to-Phase Voltage. See also Rules 239E1 and 239E2b.) 



I 



Clearance of open vertical and lateral 
conductors 


to 8.7 kV 
(in) 


Over 8.7 to 50 kV 

(in) 


Over 50 kV 4 

(in) 


From surfaces of supports 


3 1 - 2 


3 plus 0.2 per kV 
over 8.7 kV 


11 plus 0.2 per kV 
over 50 kV 


From span, guy, and messenger wires 5 


6 


6 plus 0.4 per kV 
over 8.7 kV 3 


23 plus 0.4 per kV 
over 50 kV 3 



1 



A neutral conductor meeting Rule 230E1 may be attached directly to the structure surface. 



^ For supply circuits of to 750 V, this clearance may be reduced to 1 in. 

^ Multiplier may be reduced to 0.25 in/kV for anchor guys. 

^ The additional clearance for voltages in excess of 50 kV specified in Table 239-1 shall be increased 3% 
for each 1000 ft in excess of 3300 ft above mean sea level. 

5 These clearances may be reduced by not more than 25% to a guy insulator, provided that full clearance 
is maintained to its metallic end fittings and the guy wires. The clearance to an insulated section of a guy 
between two insulators may be reduced by not more than 25% provided that full clearance is maintained to 
the uninsulated portion of the guy. 



153 
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T-239-2(m) 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-239-2(in) 



m 



Table 239-2 
| Clearance Between Open Vertical Conductors and Pole Surface 

[Voltages are phase to ground for effectively grounded circuits and those other circuits where all ground 

faults are cleared by promptly de-energizing the faulted section, both initially and following subsequent 

breaker operations. See the definitions section for voltages of other systems. 

See also Rule 239E2a(l) and 239E2a(2).] 



Voltage 

(kV) 


Distance above and below open supply 
conductors where clearances apply 

(m) 


Clearance between vertical 

conductor and pole surface 

(mm) 


0to22 


1.80 


480 


22 to 30 


1.80 


560 


30 to 50 


1.80 


760 



in 



Table 239-2 
| Clearance Between Open Vertical Conductors and Pole Surface 

[Voltages are phase to ground for effectively grounded circuits and those other circuits where all ground 

faults are cleared by promptly de-energizing the faulted section, both initially and following subsequent 

breaker operations. See the definitions section for voltages of other systems. 

See also Rule 239E2a(l) and 239E2a(2).] 



Voltage 

(kV) 


Distance above and below open supply 
conductors where clearances apply 

(ft) 


Clearance between vertical 
conductor and pole surface 

(in) 


0to22 


6 


19 


22 to 30 


6 


22 


30 to 50 


6 


30 



154 
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240 PART 2. SAFETY RULES FOR OVERHEAD LINES 242 



Section 24. 
Grades of Construction 

240. General 

A. The grades of construction are specified in this section on the basis of the required strengths for safety. 
Where two or more conditions define the grade of construction required, the grade used shall be the 
highest one required by any of the conditions. 

B. For the purposes of this section, the voltage values for direct-current circuits shall be considered 
equivalent to the rms values for alternating-current circuits. 

241. Application of Grades of Construction to Different Situations 

A. Supply Cables 

For the purposes of these rules, supply cables are classified by two types as follows: 

Type 1 — Supply cables conforming to Rules 230C1, 230C2, or 230C3 shall be installed in accor- 
dance with Rule 2611. 

Type 2 — All other supply cables are required to have the same grade of construction as open- wire 
conductors of the same voltage. 

B. Order of Grades 

The relative order of grades for supply and communication conductors and supporting structures is 
B, C, and N, with Grade B being the highest. 

C. At Crossings 

Wires, conductors, or other cables of one line are considered to be at crossings when they cross over 
another line, whether or not on a common supporting structure, or when they cross over or overhang 
a railroad track or the traveled way of a limited access highway. Joint-use or collinear construction 
in itself is not considered to be at crossings. 

1 . Grade of Upper Line 

Conductors and supporting structures of a line crossing over another line shall have the grade of 
construction specified in Rules 241C3, 242, and 243. 

2. Grade of Lower Line 

Conductors and supporting structures of a line crossing under another line need only have the 
grades of construction that would be required if the line at the higher level were not there. 

3. Multiple Crossings 

a. Where a line crosses in one span over two or more other lines, or where one line crosses over 
a span of a second line, which span in turn crosses a span of a third line, the grade of construc- 
tion of the uppermost line shall be not less than the highest grade that would be required of 
either one of the lower lines when crossing the other lower line. 

b. Where communication conductors cross over supply conductors and railroad tracks in the 
same span, the grades of construction shall be in accordance with Grade B construction. It is 
recommended that the placing of communication conductors above supply conductors 
generally be avoided unless the supply conductors are trolley-contact conductors and their 
associated feeders. 

D. Conflicts (see Section 2, Structure Conflict) 

The grade of construction of the conflicting structure shall be as required by Rule 243A4. 

242. Grades of Construction for Conductors 

The grades of construction required for conductors are given in Tables 242-1 and 242-2. For the pur- 
pose of these tables certain classes of circuits are treated as follows: 

155 
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I 



242A PART 2. SAFETY RULES FOR OVERHEAD LINES 242F 



A. Constant-Current Circuit Conductors 

The grade of construction for conductors of a constant-current supply circuit involved with a 
communication circuit and not in Type 1 cable shall be based on either its current rating or on the 
open-circuit voltage rating of the transformer supplying such circuit, as set forth in Tables 242-1 and 
242-2. When the constant current supply circuit is in Type 1 cable, the grade of construction shall be 
based on its nominal full-load voltage. 

B. Railway Feeder and Trolley-Contact Circuit Conductors 

Railway feeder and trolley-contact circuit conductors shall be considered as supply conductors for 
the purpose of determining the required grade of construction. 

C. Communication Circuit Conductors Located in the Supply Space 

Communication circuit conductors located in the supply space shall have their grade of construction 
determined as follows: 

1 . Circuits meeting the requirements of Rule 224 A3 may have the same grade of construction as or- 
dinary communication circuits. 

2. Circuits not meeting the requirements of Rule 224A3 shall have the same grade of construction 
as the supply circuits above which they are located. 

D. Fire- Alarm Circuit Conductors 

Fire-alarm circuit conductors shall meet the strength and loading requirements of communication cir- 
cuit conductors. 

E. Neutral Conductors of Supply Circuits 

Supply-circuit neutral conductors, which are effectively grounded throughout their length and are not 
located above supply conductors of more than 750 V to ground, shall have the same grade of con- 
struction as supply conductors of not more than 750 V to ground, except that they need not meet any 
insulation requirements. Other neutral conductors shall have the same grade of construction as the 
phase conductors of the supply circuits with which they are associated. 

F. Surge-Protection Wires 

Surge-protection wires shall be of the same grade of construction as the supply conductors with which 
they are associated. 



156 
Copyright © 2001 IEEE. All rights reserved. 



T-242-1 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-242-1 



Table 242-1 

Grades of Construction for Supply Conductors Alone, 

at Crossing, or on the Same Structures With Other Conductors 

(The voltages listed in this table are phase-to-ground values for: effectively grounded ac circuits, two-wire 

grounded circuits, or center-grounded dc circuits; otherwise phase-to-phase values shall be used. The grade 

of construction for supply conductors, as indicated across the top of the table, shall also meet the requirements 

for any lines at lower levels except when otherwise noted.) 



Conductors, 

tracks, and 

rights-of-way 

at lower levels 


Supply conductors at higher levels 


Constant-potential supply conductors 


Constant- 
current 
supply 
conductors 


Communication 

conductors 

located in the 

supply space 


Oto 
750 V 


751 V to 
8.7 kV 


Exceeding 
8.7 kV 


Urban 


Rural 


Urban 


Rural 


Urban 


Rural 


Open 

or 
Cable 


Open 

or 
Cable 


Open 


Cable 


Open Cable 


Open Cable 


Open 


Cable 


Open 


Cable 


Open 

or 
Cable 


Exclusive 

private 

rights-of-way 


N 


N 


N 2 


N 


N N 


N 2 N 2 


N 


N 


B, C, or N; 
see Rule 

242A 


CorN; 
see Rule 242C 


Common or 
public rights-of- 
way 


N 


N 


C 


N 


N N 


C 3 C 


N 


N 


Railroad tracks 
and limited- 
access 
highways 11 


B 


B 


B 


B 


B B 


B B 


B 


B 


B 


B 


B 


Constant- 
potential supply 
conductors 

to 750 V, 
open or cable 


N 


N 


C 


N 


N N 


C 3 C 


C 4 


N 


B.C.orN; 
see Rule 

242A 


B, C, or N; 
see Rule 242C 


750 V to 8.7 kV 
Open 


C 5 


N 


C 


C 


N N 


C 3 C 


N 


N 


Cable 


N 


N 


C 


N 


N N 


C 3 C 


N 


N 


Exceeding 
8.7 kV 
Open 


B 5 


C 5 


B 


B 


N N 


C 3 c 


N 


N 


Cable 


C 5 


N 


C 


N 


N N 


c 3 c 


N 


N 


Constant- 
current supply 
conductors: 
open or cable 


B, C, or N; see Rule 242A 


B, C.orN: 

see Rule 

242A 


B, C, or N; 

see Rules 242A 

and 242C 


Communication 
conductors: 

open or cable, 
located in the 
supply space 


B, C, or N; see Rule 242C 


B, C, or N; 

see Rules 

242A and 

242C 


B, C, or N; see 
Rule 242C 


Communication 
conductor: 
urban or rural, 
open or cable 


N 


N 


B 7,8 


C 


B 7 ' 8 C 


B 8 C 


B 8 


C 


B 8,9 


Cor 

N;see 
Rule 
242A 


B,C, orN; 
see Rule 242C 






157 
Copyright © 2001 IEEE. All rights reserved. 



T-242- 1 PART 2. SAFETY RULES FOR OVERHEAD LINES T-242- 1 



The words "open" and "cable" appearing in the headings have the following meanings as applied to sup- 
ply conductors: Cable means the Type 1 cables described in Rule 241 A; Open means Type 2 cables described 
in Rule 241 A and open wire. 

Lines that can fall outside the exclusive private rights-of-way shall comply with the grades specified for 
lines not on exclusive private rights-of-way. 

Supply conductors shall meet the requirements of Grade B construction if the supply circuits will not be 
promptly de-energized, both initially and following subsequent breaker operations, in the event of a contact 
with lower supply conductors or other grounded objects. 

Grade N construction may be used if crossing over supply services only. 
^ If the wires are service drops, they may have Grade N sizes and tensions as set forth in Table 263-2. 

Grade N construction may be used where the communication conductors consist only of not more than 
one insulated twisted-pair or parallel-lay conductor, or where service drops only are involved. 

Grade C construction may be used if the voltage does not exceed 5.0 kV phase to phase or 2.9 kV phase 
to ground. 

The supply conductors need only meet the requirements of Grade C construction if both of the following 
conditions are fulfilled: 

(a) The supply voltage will be promptly removed from the communications plant by de-energization or 
other means, both initially and following subsequent circuit-breaker operations in the event of a contact with 
the communications plant. 

(b) The voltage and current impressed on the communications plant in the event of a contact with the sup- 
ply conductors are not in excess of the safe operating limit of the communications-protective devices. 

Grade C construction may be used if the current cannot exceed 7.5 A or the open-circuit voltage of the 
transformer supplying the circuit does not exceed 2.9 kV. 

Communication circuits located below supply conductors shall not affect the grade of construction of 
the supply circuits. 

There is no intent to require Grade B over ordinary streets and highways. 



158 
Copyright © 2001 IEEE. All rights reserved. 



T-242-2 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-242-2 



Table 242-2 
Grades of Construction for Communication Conductors Alone or in Upper Position of 

Crossing or on Joint Poles 

(The voltages listed in this table are phase-to-ground values for: effectively grounded ac circuits, two-wire 

grounded circuits, or center-grounded dc circuits; otherwise phase-to-phase values shall be used. The grade 

of construction for supply conductors, as indicated across the top of the table, shall also meet the 

requirements for any lines at lower levels except when otherwise noted.) (Placing of communication 

conductors at higher levels at crossings or on jointly used poles should generally be avoided, unless the 

supply conductors are trolley-contact conductors and their associated feeders.) 



Conductors, tracks, and rights-of-way 
at lower levels 


Communication conductors (communication 

conductors, rural or urban, open or cable, 

including those run in the supply space.) 


Exclusive private right-of-way 


N 


Common or public rights-of-way 


N 


Railroad tracks and limited-access highways 5 


B 


Constant-potential supply conductors 
to 750 V 
Open or cable 


N 


750 V to 2.9 kV 
Open or cable 


C 


Exceeding 2.9 kV 
Open 
Cable 


B 
C 


Constant-current supply conductors 
to 7.5 A 
Open 2 


C 


Exceeding 7.5 A 
Open 2 


B 3 


Communication conductors, open or cable, 
urban or rural including those run in the 
supply space 


B,C,orN 4 



I 



The words "open" and "cable" appearing in the headlines have the following meaning as applied to 
supply conductors: Cable means Type 1 cables as described in Rule 241 Al; Open means open- wire and 
also Type 2 cables, as described in Rule 241A2. 

Where constant-current circuits are in Type 1 cable, the grade of construction shall be based on the 
nominal full-load voltage. 

Grade C construction may be used if the open-circuit voltage of the transformer supplying the circuit 
does not exceed 2.9 kV. 
4 See Rule 242C. 

There is no intent to require Grade B over ordinary streets and highways. 



159 
Copyright © 2001 IEEE. All rights reserved. 



243 PART 2. SAFETY RULES FOR OVERHEAD LINES 243C5 



243. Grades of Construction for Line Supports 

A. Structures 

The grade of construction shall be that required for the highest grade of conductors supported except 
as modified by the following: 

1. The grade of construction of jointly used structures, or structures used only by communication 
lines, need not be increased merely because the communication wires carried on such structures 
cross over trolley-contact conductors of to 750 V to ground. 

2. Structures carrying supply service drops of to 750 V to ground shall have a grade of construc- 
tion not less than that required for supply line conductors of the same voltage. 

3. Where the communication lines cross over supply conductors and a railroad in the same span and 
Grade B is required by Rule 241C3b for the communication conductors, due to the presence of 
railroad tracks, the grade of the structures shall be B. 

4. The grade of construction required for a conflicting structure (first circuit) shall be determined 
from the requirements of Rule 242 for crossings. The conflicting structure's conductors (first cir- 
cuit) shall be assumed to cross the other circuit's conductors (second circuit) for the purposes of 
determining the grade of construction required for the conflicting structure. 

NOTE: The resulting structure grade requirement could result in a higher grade of construction for the struc- 
ture than for the conductors carried thereon. 

B. Crossarms and Support Arms 

The grade of construction shall be that required for the highest grade of conductors carried by the arm 
concerned except as modified by the following: 

1 . The grade of construction of arms carrying only communication conductors need not be increased 
merely because the conductors cross over trolley-contact conductors of to 750 V to ground. 

2. Arms carrying supply service drops of to 750 V to ground shall have a grade of construction not 
less than that required for supply line conductors of the same voltage. 

3. Where communication lines cross over supply conductors and a railroad in the same span and 
Grade B is required by Rule 241C3b for the communication conductors due to the presence of 
railroad tracks, the grade of the arm shall be B. 

C. Pins, Armless Construction Brackets, Insulators, and Conductor Fastenings 

The grade of construction for pins, armless construction brackets, insulators, and conductor fasten- 
ings shall be that required for the conductor concerned except as modified by the following: 

1. The grade of construction need not be increased merely because the supported conductors cross 
over trolley-contact conductors of to 750 V to ground. 

2. Supply service drops of to 750 V to ground require only the same grade of construction as sup- 
ply-line conductors of the same voltage. 

3. When Grade B construction is required by Rule 241C3b for the communication conductors due 
to the presence of railroad tracks, Grade B construction shall be used when supporting communi- 
cation lines that cross over supply conductors and a railroad in the same span. 

4. When communication conductors are required to meet Grade B or C, only the requirements for 
mechanical strength for these grades are required. 

5. Insulators for use on open conductor supply lines shall meet the requirements of Section 27 for 
all grades of construction. 



160 
Copyright © 2001 IEEE. All rights reserved. 



250 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



250C 



Section 25. 
Loadings for Grades B and C 

250. General Loading Requirements and Maps 

A. General 

1. It is necessary to assume the wind and ice loads that may occur on a line. Two weather loadings 
are specified in Rules 250B and 250C. Where both rules apply, the required loading shall be the 
one that has the greater effect. 

2. Where construction or maintenance loads exceed those imposed by Rule 250A1 , which may occur 
more frequently in light loading areas, the assumed loadings shall be increased accordingly. 

3. It is recognized that loadings actually experienced in certain areas in each of the loading districts 
may be greater, or in some cases, may be less than those specified in these rules. In the absence of 
a detailed loading analysis, no reduction in the loadings specified therein shall be made without 
the approval of the administrative authority. 

4. The structural capacity provided by meeting the loading and strength requirements of Sections 25 
and 26 provides sufficient capability to resist earthquake ground motions. 

B. Combined Ice and Wind Loading 

Three general degrees of loading due to weather conditions are recognized and are designated as 
heavy, medium, and light loading. Figure 250-1 shows the districts where these loadings apply. 
NOTE: The localities are classified in the different loading districts according to the relative simultaneous prev- 
alence of the wind velocity and thickness of ice that accumulates on wires. Light loading is for places where little, 
if any, ice accumulates on wires. 

Table 250-1 shows the radial thickness of ice and the wind pressures to be used in calculating loads. 
Ice is assumed to weigh 913 kg/m 3 (57 lb/ft 3 ) 

C. Extreme Wind Loading 

If no portion of a structure or its supported facilities exceeds 18m (60 ft) above ground or water level, 
the provisions of this rule are not required, except as specified in Rule 261 Ale or Rule 261 A2f. Where 
a structure or its supported facilities exceeds 18 m (60 ft) above ground or water level the structure 
and its supported facilities shall be designed to withstand the extreme wind load associated with the 
Basic Wind Speed, as specified by Figure 250-2. The wind pressures calculated shall be applied to the 
entire structure and supported facilities without ice. The following formula shall be used to calculate 
wind load. 

Load in newtons = 0.613 • (V^) 2 • k z • Grp ■ I • C d • A(m 2 ) 

Load in pounds = 0.00256 • (V mi/h ) 2 • k z • Grf ■ I ■ C d • A(ft 2 ) 



where: 



0.613 Ambient Air Density Value, the Constants 0.613, metric, 

0.00256 and 0.00256, English, reflects the mass density of air for 

the standard atmosphere, i.e., temperature of 15 °C (59 °F) 

and sea level pressure of 760 mm (29.92 in) of mercury, 
k z Velocity Pressure Exposure Coefficient, as defined in 

Rule 250C1, Table 250-2, 
V Basic Wind Speed, 3 s gust wind speed in m/s at 10 m 

(mi/h at 33 ft) above ground, Figure 250-2, 
Grp Gust Response Factor, as defined in Rule 250C2, 

I Importance Factor, 1 .0 for utility structures and their 

supported facilities, 
C d Shape Factor, as defined in Rule 252B, 

A Projected wind area, m 2 (ft 2 ). 



161 
Copyright © 2001 IEEE. All rights reserved. 



F-250-1 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-250-1 



HAWAII -LIGHT V.k V 
ALASKA-HEAVY \) 




Fig 250-1 

General Loading Map of United States 

with Respect to Loading of Overhead Lines 



Table 250-1 
Ice, Wind, and Temperature 





Loading districts (For use with Rule 250B) 


Extreme wind loading 

(For use with Rule 

250C) 


Heavy 


Medium 


Light 


Radial thickness of ice 
(mm) 


12.5 


6.5 








(in) 


0.50 


.;: '■'. .; 0.25.; :■..;.; x';, ■ o . : ;'■■■{■ ;■..■ /■:■■:■ :-q.-/'; : . . . 


Horizontal wind pressure 
(Pa) 


190 


190 


430 


See Fig 250-2 


Qb/ffi) :. ;--' :: --: : ':':7\ / ... . '4 : ■ : : '[ .' : ::;< : : '. [ ; T '9V x;;.-. : , .See Fig 250.2; : '. : '-,- 


Temperature 
(°Q 


-20 


-10 


-1 


+15 


'■': '■("¥)■ fmW^r^ : S^ 1 ■ '■ . ■ . ' 1 '■:":■■ '+16-:':' ■ ■.[■■ ■ '• . +30 ■ 1 . . ■ ' ' . ' - : ,; +60 : : "■■'■' ' 

I | ( '' | 



162 
Copyright © 2001 IEEE. All rights reserved. 



250C 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-250-2 



The wind pressure parameters (k z , V, and Grp) are based on open terrain with scattered obstructions 
(Exposure Category C as defined in ASCE 7-98). Exposure Category C is the basis of the NESC ex- 
treme wind criteria. Topographical features such as ridges, hills, and escarpments may increase the 
wind loads on site-specific structures. A Topographic Factor, K zt , from ASCE 7-98 may be used to 
account for these special cases. 

1 . Velocity Pressure Exposure Coefficient, k z 

The k z for the structure is based on the total structure height, h, above the groundline. The k z for 
the wire is based on the height, h, of the wire at the structure. The numerical values of k z , for values 
of structure and conductor height are tabulated in Table 250-2. In special terrain conditions (i.e., 
mountainous terrain and canyon) where the height of the conductor above ground at mid-span may 
be substantially higher than at the attachment point, engineering judgment may be used in deter- 
mining an appropriate value for the wire k z . The value of k z may also be determined using the for- 
mulas in Table 250-2. When h is > 75 m (250 ft) the formulas shall be used to determine a k z value. 

2. Gust Response Factor, Grf 

The structure and wire gust response factors are tabulated in Table 250-3. The structure Gust 
Response Factor, Grp, is determined using the total structure height, h. The wire Gust Response 
Factor is determined using the height of the wire at the structure, h, and the design wind span, L. 
The structure and wire gust response factors may also be determined using the formulas in Table 
250-3. For values of h > 75 m (250 ft) and L > 600 m (2000 ft) the Grf shall be determined using 
the formulas in Table 250-3. In special terrain conditions (i.e., mountainous terrain and canyon) 
where the height of the conductor above ground at midspan may be substantially higher than at 
the attachment point, engineering judgment may be used in determining an appropriate value for 
the wire G^p. Wire attachment points that are 1 8 m (60 ft) or less above ground or water level must 
be considered if the total structure height is greater than 18 m (60 ft) above ground or water. 

Table 250-2 
Velocity Pressure Exposure Coefficient k z , Structure and Wire 



Height, h (m) 


Height, h (ft) 


k z (Structure) 


k z (Wire) 


<10 


< 33 

> "45 to 50 


0.92 


1.00 


> 10 to 15 


1.00 


1.10 


> 15 to 25 


> 50 to 80 


1.10 


1.20 


> 25 to 35 


,•'80 to 115 
:- IIS in 365 
> 165 to 250 


1.20 


1.30 


> 35 to 50 


1.30 


1.40 


> 50 to 75 


1.40 


1.50 


>75 


■ 250 


Use Formulas 


Use Formulas 


Formulas (Metric): 

Structure k z = 2.01 ■ (0.67 • h/275) ( 

Wire k z = 2.01 • (h/275) (2/95) 


2/9.5) 


forl8m<h<275m 
for 10 m < h < 275 m 


Formulas (English): 

Shiicture :/ : V ."': k z = 2:01 ■ (6,67 : h/900); ( 

Wire k z =2.01 • <h/900) ilN M 


2/9.5): '.. ■ ■.'■ :■■■'.■.'■ ■ 


foi 60 ft < h < 900 ft 
for 33 ft < h < 900 ft 


h = Structure or Wire height as defined in Rule 250C1 

Minimum k z =0.85 

Formulas are for Exposure Category C, ASCE 7-98 



163 
Copyright © 2001 IEEE. All rights reserved. 



T-250-3(m) 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-250-3(m) 



m 



Table 250-3 
Structure and Wire Gust Response Factors, Grp 





Height 


Structure 


Wire Grj-, Span Length, L (m) 




h(m) 


G RF 


<75 


75<L<150 


150<L<225 


225<L<300 


300<L<450 


450<L<600 


L>600 




<10 


1.02 


0.93 


0.86 


0.79 


0.75 


0.73 


0.69 






> 10 to 15 


0.97 


0.88 


0.82 


0.76 


0.72 


0.70 


0.67 






> 15 to 25 


0.93 


0.86 


0.80 


0.75 


0.71 


0.69 


0.66 






> 25 to 35 


0.89 


0.83 


0.78 


0.73 


0.70 


0.68 


0.65 






> 35 to 50 


0.86 


0.82 


0.77 


0.72 


0.69 


0.67 


0.64 






> 50 to 75 


0.83 


0.80 


0.75 


0.71 


0.68 


0.66 


0.63 






>75 


(1) 


(1) 


(1) 


(1) 


(1) 


(1) 


0) 




i 
i 


Formulas: Where: 

Structure Grf = [1 + (2.7 ■ E s • B s 0,5 )]/k v E w =Wire Exposure Factor 

Wire Grf = [1 + (2.7 • E w ■ B w ° 5 )]/k v 2 E s = Structure Exposure Factor 

B w = Dimensionless response term corresponding to the quasi-static 
E s = 0.346- [10/(0.67 • h)] 1 ' 7 background wind loads on the wire 

B s = Dimensionless response term corresponding to the quasi-static 
E w = 0.346 • (10/h) background wind loads on the structure 

B s = 1/(1 + 0.375 • h/67) k v =1.43 

B w = 1/(1 + 0.8 • L/67) h = Structure or Wire height, as defined in Rule 250C2, in meters 

L = Design Wind Span, in meters 
Formulas are for Exposure Category C, ASCE 7-98 
(1) For heights greater than 75 m and/or spans greater than 600 m, the formulas shall be used 



164 
Copyright © 2001 IEEE. All rights reserved. 



T-250-3(ft) 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-250-3(ft) 



ft 



Table 250-3 
Structure and Wire Gust Response Factors, Grf 





Height 


Structure 


Wire Grf, Span Length, L (ft) 




h(ft) 


Grf 


<250 


250<L<500 


500<L<750 


750<L<1000 


1000<L<1500 


1500<L<2000 


L>2000 1 




<33 


1.02 


0.93 


0.86 


0.79 


0.75 


0.73 


0.69 






> 33 to 50 


0.97 


0.88 


0.82 


0.76 


0.72 


0.70 


0.67 






> 50 to 80 


0.93 


0.86 


0.80 


0.75 


0.71 


0.69 


0.66 






> 80 to 115 


0.89 


0.83 


0.78 


0.73 


0.70 


0.68 


0.65 






>115tol65 1 


0.86 


0.82 


0.77 


0.72 


0.69 


0.67 


0.64 






> 165 to 250 


0.83 


0.80 


0.75 


0.71 


0.68 


0.66 


0.63 






>250 


(1) 


(1) 


(1) 


(1) 


(1) 


(1) 


(1) 




i 
i 


Formulas: Where: 

Structure Grf = [1 + (2.7 • E s ■ B s a5 )]/k v 2 E w = Wire Exposure Factor 

Wire Grf = [1 + (2.7 ■ E w • B w 05 )]/k v 2 E s = Structure Exposure Factor 

B w = Dimensionless response term corresponding to the quasi-static 
E s = 0.346 • [33/(0.67 • h)] 1/7 background wind loads on the wire 

B s = Dimensionless response term corresponding to the quasi-static 
E w = 0.346 • (33/h) 1/7 background wind loads on the structure 

B s = 1/(1 + 0.375 • h/220) k v = 1.43 

B w = 1/(1 + 0.8 • L/220) h = Structure or Wire height, as defined in Rule 250C2, in feet 

L = Design Wind Span, in feet 
Formulas are for Exposure Category C, ASCE 7-98 
(1) For heights greater than 250 ft and/or spans greater than 2000 ft, the formulas shall be used 



165 
Copyright © 2001 IEEE. All rights reserved. 



F-250-2(a) 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



F-250-2(a) 




-140 



Fig 250-2(a) 
Basic Wind Speeds* 

*Fig 250-2(a) reprinted with the permission of ASCE Publications, 1801 Alexander Bell Dr., Reston, V A 20191 from 
ASCE 7-98, Minimum Design Loads for Buildings and Other Structures. Copyright © 1998. 



166 
Copyright © 2001 IEEE. All rights reserved. 



F-250-2(b) 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



F-250-2(b) 




90(40) 
100(45) 



130(58) 
140(63) 

150(67) 



90(40) 
100(45) 



130(58) 



110(49)120(54) 



Location 
Hawaii 
Puerto Rico 
Guam 

Virgin Islands 
American Samoa 



Vmph 
105 

145 
170 
145 
125 



(m/s) 

(47) 

(65) 

(76) 

(65) 

(56) 



Notes: 

1. Values are nominal design 3-second gust wind speeds in miles per hour (m/s) 
at 33 ft (10 m) above ground for Exposure C category. 

2. Linear interpolation between wind contours is permitted. 

3. Islands and coastal areas outside the last contour shall use the last wind speed 
contour of the coastal area. 

4. Mountainous terrain, gorges, ocean promontories, and special wind regions 
shall be examined for unusual wind conditions. 



Fig 250-2(b) 
Basic Wind Speeds'" 

"*Fig 250-2(b) reprinted with the permission of ASCE Publications, 1801 Alexander Bell Dr., Reston, VA 20191 from 
ASCE 7-98, Minimum Design Loads for Buildings and Other Structures. Copyright © 1998. 



167 
Copyright © 2001 IEEE. All rights reserved. 



F-250-2(c) 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



F-250-2(c) 




130(58) 



110(49)120(54) 



Notes: 

1. Values are nominal design 3-second gust wind 
speeds In miles per hour {wit) at 33 ft (10 m) 
above ground for Exposure C category. 
Linear interpolation between wind contours Is 
permitted. 

3. Islands and coastal areas outside the last 
contour shall use the last wind speed contour 
of the coastal area. 
Mountainous terrain, gorges, ocean 
promontories, and special wind regions shall 
be examined for unusual wind conditions. 



Fig 250-2(c) 
Western Gulf of Mexico Hurricane Coastline* 

*Fig 250-2(c) reprinted with the permission of ASCE Publications, 1801 Alexander Bell Dr., Reston, VA 20191 from 
ASCE 7-98, Minimum Design Loads for Buildings and Other Structures. Copyright © 1998. 



168 
Copyright © 2001 IEEE. All rights reserved. 



F-250-2(d) 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



F-250-2(e) 




.130(58) 
.140(63) 



Special Wind Region 



120(54) 
130(55) 



1 . Values are nominal design 3-second gust wind 
speeds In miles per hour (m/s) at 33 ft (10 m) 
above ground for Exposure C category. 

2. Linear Interpolation between wind contours Is 
permitted. 

3. Islands and coastal areas outside the last 
contour shall use the last wind speed contour 
of the coastal area. 

4. Mountainous terrain, gorges, ocean 
promontories, and special wind regions shall 
be examined for unusual wind conditions. 



150(67) 



Fig 250-2(d) 
Eastern Gulf of Mexico and Southeastern US Hurricane Coastline* 



• 




Special Wind Region 



Notes: 

1. Values are nominal design 3-second gust wind 
In miles per hour (nvs) at 33 ft (10 m) 

above ground for Exposure C category. 

2. Linear interpolation between wind contours Is 
permitted, 

3. Islands and coastal anas outside the last 
contour shall use the last wind speed contour 
of the coastal area 

4. Mountainous terrain, gorges, ocean 
promontories, and special wind regions shall 
be examined for unusual wind conditions. 



Fig 250-2(e) 
Mid and Northern Atlantic Hurricane Coastline* 

*Fig 250-2(d) and Fig 250-2(e) reprinted with the permission of ASCE Publications, 1801 Alexander Bell Dr., Reston, 
VA 20191 from ASCE 7-98, Minimum Design Loads for Buildings and Other Structures. Copyright © 1998. 



169 

Copyright © 2001 IEEE. All rights reserved. 



251 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-251-1 



251. Conductor Loading 

A. General 

Ice and wind loads are specified in Rule 250. 

1 . Where a cable is attached to a messenger, the specified loads shall be applied to both cable and 
messenger. 

2. In determining wind loads on a conductor or cable without ice covering, the assumed projected 
area shall be that of a smooth cylinder whose outside diameter is the same as that of the conductor 
or cable. The shape factor for cylindrical surfaces is assumed to be 1.0. 

NOTE: Experience has shown that as the size of multiconductor cable decreases, the actual projected area 
decreases, but the roughness factor increases and offsets the reduction in projected area. 

3. An appropriate mathematical model shall be used to determine the wind and weight loads on ice- 
coated conductors and cables. In the absence of a model developed in accordance with Rule 
251A4, the following mathematical model shall be used: 

a. On a conductor, lashed cable, or multiple-conductor cable, the coating of ice shall be 
considered to be a hollow cylinder touching the outer strands of the conductor or the outer 
circumference of the lashed cable or multiple-conductor cable. 

b. On bundled conductors, the coating of ice shall be considered as individual hollow cylinders 
around each subconductor. 

4. It is recognized that the effects of conductor stranding or of non-circular cross section may result 
in wind and ice loadings more or less than those calculated according to assumptions stated in 
Rule 251A2 and Rule 251 A3. No reduction in these loadings is permitted unless testing or a qual- 
ified engineering study justifies a reduction. 

B. Load Components 

The load components shall be determined as follows: 

1 . Vertical Load Component 

The vertical load on a wire, conductor, or messenger shall be its own weight plus the weight of 
conductors, spacers, or equipment that it supports, ice covered where required by Rule 250. 

2. Horizontal Load Component 

The horizontal load shall be the horizontal wind pressure determined under Rule 250 applied at 
right angles to the direction of the line using the projected area of the conductor or messenger and 
conductors, spacers, or equipment that it supports, ice covered where required by Rule 250. 

3. Total Load 

The total load on each wire, conductor, or messenger shall be the resultant of components 1 and 2 
above, calculated at the applicable temperature in Table 251-1, plus the corresponding constant in 
Table 251-1. In all cases the conductor or messenger tension shall be computed from this total load. 



Table 251-1 
Temperatures and Constants 





Loading districts (for use with Rule 250B) 


Extreme wind 
loading (for use 
with Rule 250C) 


Heavy 


Medium 


Light 


Temperature (°C) 


-20 


-10 


-1 


+ 15 


:-'.. ':':;-;. ■'■;■ I'-. (°F):.| ■.:'■.'. JV ■ '0-': : ---- : -:-:'1. x :-. ' /.+15 : '. . : '. : V ■ 


i : ; ■ '. : .;+.3bv';:;.. ■.■'■-■'■. +60 '■:■ ■ ';' ■ 


Constant to be 
added to the 
resultant 
(all conductors) 
inN/m 


4.4 


2.9 


0.73 


0.0 


■ : ■: in lb/ft ■■■.';,■ A '■■ ' :.'. : 0.3Q :.■'■.■■ : ' : " v|\; ■ :vP.2P;:;;.^^'^'|.^■ -0.Q5 /^ : ■; . ; ; /[' ^0 0,0 .■■'.'■'■ ■:■: 



170 
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252 PART 2. SAFETY RULES FOR OVERHEAD LINES 252C 1 



252. Loads on Line Supports 

A. Assumed Vertical Loads 

The vertical loads on poles, towers, foundations, crossarms, pins, insulators, and conductor fastenings 
shall be their own weight plus the weight that they support, including all wires and cables, in accor- 
dance with Rules 25 1 A and 25 IB 1, together with the effect of any difference in elevation of supports. 
Loads due to radial ice shall be computed on wires, cables, and messengers, but need not be computed 
on supports. 

B. Assumed Transverse Loads 

The total transverse loads on poles, towers, foundations, crossarms, pins, insulators, and conductor 
fastenings shall include the following: 

1. Transverse Loads from Conductors and Messengers 

The transverse loads from conductors and messengers shall be the horizontal load determined by 
Rule 251. 

EXCEPTION: In medium- and heavy-loading districts, where supporting structures carry ten or more con- 
ductors on the same crossarm, not including cables supported by messengers, and where the horizontal pin 
spacing does not exceed 380 mm (15 in), the transverse wind load may be calculated on two-thirds of the 
total number of such conductors if at least ten conductors are used in the calculations. 

2. Wind Loads on Structures 

The transverse load on structures and equipment shall be computed by applying, at right angles to 
the direction of the line, the appropriate horizontal wind pressure determined under Rule 250. This 
load shall be calculated using the projected surfaces of the structures and equipment supported 
thereon, without ice covering. The following shape factors shall be used. 

a. Cylindrical Structures and Components 

Wind loads on straight or tapered cylindrical structures or structures composed of numerous 
narrow relatively flat panels that combine to form a total cross section that is circular or ellip- 
tical in shape shall be computed using a shape factor of 1.0. 

b. Flat Surfaced (Not Lattice) Structures and Components 

Wind loads on flat surfaced structures, having solid or enclosed flat sides and an overall cross 
section that is square or rectangular, shall be computed using a shape factor of 1.6. 

c. Lattice Structures 

Wind loads on square or rectangular lattice structures or components shall be computed using 
a shape factor of 3 .2 on the sum of the proj ected areas of the members of the front face if struc- 
tural members are flat surfaced or 2.0 if structural surfaces are cylindrical. The total, however, 
need not exceed the load that would occur on a solid structure of the same outside dimension. 
EXCEPTION: The shape factors listed under Rules 252B2a, 252B2b, and 252B2c may be reduced if 
wind tunnel tests or aerodynamic analysis justifies a reduction. 

3. At Angles 

Where a change in direction of wires occurs, the loads on the structure, including guys, shall be 
the vector sum of the transverse wind load and the wire tension load. In calculating these loads, a 
wind direction shall be assumed that will give the maximum resultant load. Proper reduction may 
be made to the loads to account for the reduced wind pressure on the wires resulting from the an- 
gularity of the application of the wind on the wire. 

4. Span Lengths 

The calculated transverse load shall be based on the average of the two spans adjacent to the struc- 
ture concerned. 

C. Assumed Longitudinal Loading 

1 . Change in Grade of Construction 

The longitudinal loads on supporting structures, including poles, towers, and guys at the ends of 
sections required to be of Grade B construction, when located in lines of lower than Grade B con- 
struction, shall be taken as an unbalanced pull in the direction of the higher grade section equal to 
the larger of the following values: 

171 
Copyright © 2001 IEEE. All rights reserved. 






252Cla PART 2. SAFETY RULES FOR OVERHEAD LINES 253 



a. Conductors with Rated Breaking Strength of 13.3 kN (3000 lb) or less 

The pull of two-thirds, but not less than two, of the conductors having a rated breaking strength 
of 13.3 kN (3000 lb) or less. The conductors selected shall produce the maximum stress in the 
support. 

b. Conductors with Rated Breaking Strength of more than 13.3 kN (3000 lb) 

The pull resulting from one conductor when there are eight or less conductors (including over- 
head ground wires) having rated breaking strength of more than 13.3 kN (3000 lb), and the 
pull of two conductors when there are more than eight conductors. The conductors selected 
shall produce the maximum stress in the support. 

2. Jointly Used Poles at Crossings Over Railroads, Communication Lines, or Limited Access 
Highways 

Where a joint line crosses a railroad, a communication line, or a limited access highway, and 
Grade B is required for the crossing span, the tension in the communication conductors of the joint 
line shall be considered as limited to one-half their rated breaking strength, provided they are 
smaller than Stl WG No. 8 if of steel, or AWG No. 6 if of copper. 

3. Deadends 

The longitudinal load on a supporting structure at a deadend shall be an unbalanced pull equal to 
the tensions of all conductors and messengers (including overhead ground wires); except that with 
spans in each direction from the dead-end structure, the unbalanced pull shall be the difference in 
tensions. 

4. Unequal Spans and Unequal Vertical Loads 

The structure should be capable of supporting the unbalanced longitudinal load created by the dif- 
ference in tensions in the wires in adjacent spans caused by unequal vertical loads or unequal 
spans. 

5. Stringing Loads 

Consideration should be given to longitudinal loads that may occur on the structure during wire 
stringing operations. 

6. Longitudinal Capability 

It is recommended that structures having a longitudinal strength capability be provided at reason- 
able intervals along the line. 

7. Communication Conductors on Unguyed Supports at Railroad and Limited Access Highway 
Crossings 

The longitudinal load shall be assumed equal to an unbalanced pull in the direction of the crossing 
of all open-wire conductors supported, the pull of each conductor being taken as 50% of its rated 
breaking strength in the heavy loading district, 33-1/3% in the medium loading district, and 22-1/4% 
in the light-loading district. 

D. Simultaneous Application of Loads 

Where a combination of vertical, transverse, or longitudinal loads may occur simultaneously, the 
structure shall be designed to withstand the simultaneous application of these loads. 
NOTE: Under the extreme wind conditions of Rule 250C, an oblique wind may require greater structural strength 
than that computed by Rules 252B and 252C. 

| 253. Overload Factors for Structures, Crossarms, Support Hardware, Guys, Foundations, and 
Anchors 

Loads due to the combined ice and wind loads in Rule 250B and the extreme wind loading condition 
in Rule 250C shall be multiplied by the overload factors in Table 253-1 or the alternate overload fac- 
tors in Table 253-2. Table 253-1 shall be used with Table 261-1 A. Table 253-2 shall be used with 
Table 261-1B. 

For wood and reinforced (not prestressed) concrete, two methods for determining the capacity are 
included herein. Either method meets the basic requirements for safety. 

172 
Copyright © 2001 IEEE. All rights reserved. 



T-253-1 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-253-1 



Table 253-1 

Overload Factors for Structures, 1 Crossarms, 

Support Hardware, Guys, Foundations, and Anchors to Be Used 

with the Strength Factors of Table 261-1A 



Overload Factors 




Grade B 


Grade C 


Rule 250B Loads 

Vertical Loads 3 


1.50 


1.90 6 


Transverse Loads 
Wind 
Wire Tension 


2.50 
1.65 2 


2.20 4 
1.30 5 


Longitudinal Loads 
At Crossings 
In general 
At deadends 

Elsewhere 
In general 
At deadends 


1.10 
1.65 2 

1.00 

1.65 2 


no requirement 
1.30 5 

no requirement 
1.30 5 


Rule 250C Loads 


1.00 


1.00 



* Includes pole. 

^ For guys and anchors associated with structures supporting communication conductors and cables only, 
this factor may be reduced to 1.33. 

^ Where vertical loads significantly reduce the stress in a structure member a vertical overload factor of 
1 .0 should be used for the design of such member. Such member shall be designed for the worst case loading. 

^ This factor may be reduced to 1 .75 when the span being supported is not at a crossing. 

5 For metal or prestressed concrete portions of structures and crossarms, guys, foundations, and anchors, 
use a value of 1.10. 

"For metal or prestressed concrete portions of structures, crossarms, guys, foundations, and anchors, use 
a value of 1.50. 



173 
Copyright © 2001 IEEE. All rights reserved. 



T-253-2 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-253-2 



Table 253-2 

Alternate Overload Factors for Wood and Reinforced (Not Prestressed) Concrete Structures 1, 5 

to Be Used with the Strength Factors of Table 261-1B 





Overload Factors 


Grade B 


Grade C 


When 
Installed 


At 
Replacement 2 ' 3 


When 
Installed 


At 
Replacement 2 ' 3 


Rule 250B Loads 

Vertical loads 


2.20 


1.50 


2.20 


1.50 


Transverse loads 
Wind (at crossings) 
Wind (elsewhere) 
Wire tension 


4.00 
4.00 
2.00 


2.67 
2.67 
1.33 


2.67 
2.00 
1.33 


1.33 
1.33 
1.00 


Longitudinal loads 
In general 
At deadends 


1.33 
2.00 6 


1.00 
1.33 7 


No requirement 
1.33 


No requirement 
1.00 


Rule 250C Loads 


1.33 


1.00 


1.33 


1.00 



1 Includes poles. 

2 Where a wood structure is built for temporary service, the overload factors at replacement may be used 
provided the designated fiber stress is not exceeded during the life of the structure. Where a reinforced 
concrete (not prestressed) structure is built for temporary service, the overload factors at replacement may be 
used. 

3 When structure strength deteriorates to the level of the loads multiplied by the overload factors required 
at replacement, the structure shall be replaced or rehabilitated. If a structure is replaced, it shall meet the 
"when installed" overload factors at replacement. Rehabilitated portions of structures shall have overload 
factors at the time of rehabilitation greater than of those required "at replacement." 

^ Where vertical loads significantly reduce the stress in a structural member, a vertical overload factor of 
1.0 should be used for the design of such member. Such members shall be designed for the worst-case 
loading. 

3 Metal portions of a structure may be designed using the overload factors in Table 253-1. 

6 For unguyed wood poles supporting communication conductors and cables only, this factor may be 
reduced to 1.33. 

' For unguyed wood poles supporting communication conductors and cables only, this factor may be 
reduced to 1.0. 



174 
Copyright © 2001 IEEE. All rights reserved. 



260 PART 2. SAFETY RULES FOR OVERHEAD LINES 261 Aid 

Section 26. 
Strength Requirements 

260. General (see also Section 20) 

A. Preliminary Assumptions 

1. It is recognized that deformation, deflections, or displacement of parts of the structure may 
change the effects of the loads assumed. In the calculation of stresses, allowance may be made 
for such deformation, deflection, or displacement of supporting structures including poles, tow- 
ers, guys, crossarms, pins, conductor fastenings, and insulators when the effects can be evaluated. 
Such deformation, deflection, or displacement should be calculated using Rule 250 loads prior to 
application of the overload factors in Rule 253. For crossings or conflicts, the calculations shall 
be subject to mutual agreement. 

2. It is recognized that new materials may become available. While these materials are in the process 
of development, they must be tested and evaluated. Trial installations are permitted where quali- 
fied supervision is provided. 

B. Application of strength factors 

1 . Structures shall be designed to withstand the appropriate loads multiplied by the overload factors 
in Section 25 without exceeding their strength multiplied by the strength factors in Section 26. 

2. Unless otherwise specified, a strength factor of 0.80 shall be used for the extreme wind loading 
conditions specified in Rule 250C for all supported facilities. 

NOTE: The latest edition of the following documents are among those available for determining structure 
design capacity with the specified NESC loads, overload factors, and strength factors: 

ANSI/ASCE-10, Design of Latticed Steel Transmission Structures 

ASCE-91, Design of Guyed Electrical Transmission Structure 

ASCE-PCI, Guide for the Design of Prestressed Concrete Poles 

ASCE-72, Design of Steel Transmission Pole Structures 

PCI, Design Handbook-Precast and Prestressed Concrete 

ACI-318, Building Code Requirements for Structural Concrete 

IEEE Std 751-1990, Trial-Use Design Guide for Wood Transmission Structures 

AISI, Specification for the Design of Cold-Formed Steel Structural Members 

The Aluminum Association, Aluminum Design Manual 

261. Grades B and C Construction 

A. Supporting Structures 

The strength requirements for supporting structures may be met by the structures alone or with the 

aid of guys or braces or both. 

1. Metal, Prestressed-, and Reinforced-Concrete Structures 

a. These structures shall be designed to withstand the loads in Rule 252 multiplied by the appro- 
priate overload factors in Table 253-1 or Table 253-2 without exceeding the permitted load. 

b. The permitted load shall be the strength multiplied by the strength factors in Tables 261-1 A 
or 261-1B (where guys are used, see Rule 261C). 

c. All structures including those below 18 m (60 ft) shall be designed to withstand, without con- 
ductors, the extreme wind load in Rule 250C applied in any direction on the structure. 

d. Spliced and Reinforced Structures 
Reinforcements or permanent splices to a supporting structure are permitted provided they de- 
velop the required strength of the structure. 

175 
Copyright © 2001 IEEE. All rights reserved. 



I 



261A2 PART 2. SAFETY RULES FOR OVERHEAD LINES 261 A2e(4) 



2. Wood Structures 

Wood structures shall be of material and dimensions to meet the following requirements: 

a. Wood structures shall be designed to withstand the loads in Rule 252 multiplied by the appro- 
priate overload factors in Table 253-1 or 253-2, without exceeding the permitted stress level. 
NOTE: When determining a fiber stress for column loads, buckling needs to be considered. 

EXCEPTION 1: When installed, naturally grown wood poles acting as single-based structures or 
unbraced multiple-pole structures, shall meet the requirements of Rule 261 A2a without exceeding the 
permitted stress level at the ground line for unguyed poles or at the points of attachment for guyed poles. 

EXCEPTION 2: At a Grade B crossing, in a straight section of line, wood structures complying with the 
transverse strength requirements of Rule 261 A2a, without the use of transverse guys, shall be considered 
as having the required longitudinal strength, providing the longitudinal strength is comparable to the 
transverse strength of the structure. This EXCEPTION does not modify the requirements of this rule for 
deadends. 

EXCEPTION 3: At a Grade B crossing of a supply line over a highway or a communication line where 
there is an angle in the supply line, wood structures shall be considered as having the required longitu- 
dinal strength if all of the following conditions are met: 

(a) The angle is not over 20 degrees. 

(b) The angle structure is guyed in the plane of the resultant of the conductor tensions. The tension in 
this guy under the loading in Rule 252 multiplied by an overload factor of 2.0 shall not exceed the 
rated breaking strength multiplied by the strength factor in Table 261-1A. 

(c) The angle structure has sufficient strength to withstand, without guys, the transverse loading of 
Rule 252 multiplied by the appropriate overload factors in Table 253-1 or 253-2, which would exist 
if there were no angle at that structure without exceeding the permitted stress level. 

b. Permitted Stress Level 

(1) Natural Wood Pole 

The permitted stress level of natural wood poles of various species meeting the require- 
ments of ANSI 05.1-1992 shall be determined by multiplying the designated fiber stress 
set forth in that standard by the appropriate strength factors in Tables 26 1-1 A or 261- IB. 

(2) Sawn or Laminated Wood Structural Members, Crossarms, and Braces 

The permitted stress level of sawn or laminated wood structural members, crossarms, and 
braces shall be determined by multiplying the appropriate ultimate fiber stress of the ma- 
terial by the appropriate strength factors in Tables 261-1 A or 261- IB. 

c. Strength of Guyed Poles 

Guyed poles shall be designed as columns, resisting the vertical component of the tension in 
the guy plus any other vertical loads. 

d. Spliced and Reinforced Poles 

Reinforcements or permanent splices at any section along the pole are permitted provided 
they develop the required strength of the pole. 

e. Average Strength of Three Poles 

A pole (single-base structure) not individually meeting the transverse strength requirements 
will be permitted when reinforced by a stronger pole on each side, if all of the following are met: 

(1) The average strength of the three poles meets the transverse strength requirements, 

(2) The weak pole shall have not less than 75% of its required strength, 

(3) The sag and tension of the wires, conductors, and cables in the adjacent spans shall pro- 
vide adequate additional support for the weak pole, and 

(4) The average of the spans does not exceed 45 m (150 ft). 

EXCEPTION 1: The span may exceed 45 m (150 ft), but shall not be greater than 91 m (300 ft), if over- 
head guys are run between the three poles and the line section is head-guyed and back-guyed. 

An extra pole inserted in a normal span for the purpose of supporting a service drop may be ignored 
in this strength determination. 

EXCEPTION 2: This rule does not apply to crossings over railroads, communication lines, or limited 
access highways. 

176 
Copyright © 2001 IEEE. All rights reserved. 



261A2f PART 2. SAFETY RULES FOR OVERHEAD LINES 261C2 



f. All structures including those below 18 m (60 ft) shall be designed to withstand, without con- 
ductors, the extreme wind load in Rule 250C applied in any direction on the structure. 

3. Transverse Strength Requirements for Structures Where Side Guying Is Required, But Can Be 
Installed Only at a Distance 

Grade B: If the transverse strength requirements of this section cannot be met except by the use 
of side guys or special structures, and where it is physically impractical to employ side guys, the 
transverse strength requirements may be met by side-guying the line at each side of, and as near 
as practical to, the crossing, or other transversely weak structure, and with a distance between 
such side-guyed structures of not over 250 m (800 ft), provided that: 

a. The side-guyed structures for each such section of 250 m (800 ft) or less shall be designed to 
withstand the calculated transverse load due to wind on the supports and ice-covered conduc- 
tors, on the entire section between side-guyed structures. 

b. The line between such side-guyed structures shall be substantially in a straight line and the 
average span between the side-guyed structures shall not exceed 45 m (150 ft). 

c. The entire section between the structures with the required transverse strength shall comply 
with the highest grade of construction concerned in the given section, except as to the trans- 
verse strength of the intermediate poles or towers. 

Grade C: The above provisions do not apply to Grade C. 

4. Longitudinal Strength Requirements for Sections of Higher Grade in Lines of a Lower Grade 
Construction 

a. Methods of Providing Longitudinal Strength 

Grade B: The longitudinal strength requirements for sections of line of higher grade in lines 
of a lower grade (for assumed longitudinal loading, see Rule 252) may be met by placing a 
structure of the required longitudinal strength at each end of the higher grade section. 

Where this is impractical, the structures of the required longitudinal strength may be lo- 
cated away from the section of higher grade, within 150 m (500 ft) on each side and with not 
more than 250 m (800 ft) between the structures of the required longitudinal strength. This is 
permitted provided the following conditions are met: 

(1) The structures and the line between them meet the requirements for transverse strength 
and stringing of conductors of the highest grade occurring in the section, and 

(2) The line between the structures of the required longitudinal strength is approximately 
straight or suitably guyed. 

The longitudinal strength requirement of the structures may be met by using guys. 
Grade C: The above provisions do not apply to Grade C. 

b. Flexible Supports 

Grade B: When supports of the section of higher grade are capable of considerable deflection 
in the direction of the line, it may be necessary to increase the clearances required in 
Section 23 or to provide line guys or special reinforcements to reduce the deflection. 
Grade C: The above provision does not apply to Grade C. 

B. Strength of Foundations, Settings, and Guy Anchors 

Foundations, settings, and guy anchors shall be designed or be determined by experience to withstand 
the loads in Rule 252 multiplied by the overload factors in Table 253-1 without exceeding the 
permitted load. The permitted load shall be equal to the strength multiplied by the strength factors in 
Table 261-1 A. 

NOTE: Excessive movement of foundations, settings, and guy anchors or errors in settings may reduce clearanc- 
es or structure capacity. 

C. Strength of Guys and Guy Insulators 

The strength requirements for guys and guy insulators are covered under Rules 264 and 279Alc, re- 
spectively. 

1 . Metal and Prestressed-Concrete Structures 

Guys shall be considered as an integral part of the structure. 

2. Wood and Reinforced-Concrete Structures 

When guys are used to meet the strength requirements, they shall be considered as taking the en- 

177 
Copyright © 2001 IEEE. All rights reserved. 



261D PART 2. SAFETY RULES FOR OVERHEAD LINES 261D4c 



tire load in the direction in which they act, the structure acting as a strut only, except for those 
structures considered to possess sufficient rigidity so that the guy can be considered an integral 
part of the structure. 
NOTE: Excessive movement of guys may reduce clearances or structure capacity. 

D. Crossarms and Braces 

1 . Concrete and Metal Crossarms and Braces 

Crossarms and braces shall be designed to withstand the loads in Rule 252 multiplied by the over- 
load factors in Table 253-1 without exceeding the permitted load. The permitted load shall be 
equal to the strength multiplied by the strength factors in Table 261-1 A. 

2. Wood Crossarms and Braces 

a. Strength 

(1) Crossarms and braces shall be designed to withstand the loads in Rule 252 multiplied by 
the overload factors in Table 253-1 or 253-2 without exceeding their permitted stress 
level. 

(2) The permitted stress level of solid sawn or laminated wood crossarms and braces shall be 
determined by multiplying their ultimate fiber stress by the strength factors in Table 261- 
lAor261-lB. 

b. Material and Size 

Wood crossarms and braces of select Southern pine or Douglas fir shall have a cross section 
of not less than those in Table 261-2. Crossarms of other species may be used provided they 
have equal strength. 

3. Crossarms and Braces of Other Materials 

Crossarms and braces should meet the strength requirements of Rule 261D2. 

4. Additional Requirements 

a. Longitudinal Strength 

(1) General 

(a) Crossarms shall be designed to withstand a load of 3. 1 kN (700 lb) applied at the out- 
er conductor attachment point without exceeding the permitted stress level for wood 
crossarms or the permitted load for crossarms of other materials, as applicable. 

(b) At each end of a transversely weak section, as described in Rule 261 A3, the longi- 
tudinal load shall be applied in the direction of the weak section. 

(2) Methods of Meeting Rule 26 1 D2a( 1 ) 

Grade B: Where conductor tensions are limited to a maximum of 9.0 kN (2000 lb) per 
conductor, double wood crossarms having cross sections in Table 261-2 and properly as- 
sembled will comply with the longitudinal strength requirements in Rule 261D2a(l). 
Grade C: This requirement is not applicable. 

(3) Location 

At crossings, crossarms should be mounted on the face of a pole away from the crossing, 
unless special bracing or double crossarms are used. 

b. Bracing 

Crossarms shall be supported by bracing, if necessary, to support expected loads, including 
line personnel working on them. 

c. Double Crossarms or Brackets 

Grade B: Where pin-type construction is used, double crossarms, each crossarm having the 
strength required by Rule 261D2a, or a support assembly of equivalent strength shall be used 
at each crossing structure, at ends of joint use or conflict sections, at deadends, and at corners 
where the angle of departure from a straight line exceeds 20 degrees. Under similar condi- 
tions, where a bracket supports a conductor operated at more than 750 V to ground and there 
is no crossarm below, double brackets shall be used. 

EXCEPTION: The above does not apply where communication cables or conductors cross below supply 
conductors and either are attached to the same pole, or where supply conductors are continuous and of 
uniform tension in the crossing span and each adjacent span. This exception does not apply to railroad 
crossings and limited access highways except by mutual agreement. 
Grade C: The above requirement is not applicable. 

178 
Copyright © 2001 IEEE. All rights reserved. 



261E PART 2. SAFETY RULES FOR OVERHEAD LINES 261Hla 



E. Insulators 

The strength requirements for insulators are covered under Rules 277 and 279. 

F. Strength of Pin-Type or Similar Construction and Conductor Fastenings 

1. Longitudinal Strength 

a. General 

Pin-type or similar construction and ties or other conductor fastenings shall be designed to 
withstand the applicable longitudinal loads in Rule 252, multiplied by the overload factors in 
Table 253-1, or 3.1 kN (700 lb) applied at the pin, whichever is greater. 

b. Method of Meeting Rules 261Fla 

Grade B: Where conductor tensions are limited to 9.0 kN (2000 lb) and such conductors are 
supported on pin insulators, double wood pins and ties or their equivalent will be considered 
to meet the requirements of Rule 261Fla. 
Grade C: No requirement. 

c. At Deadends and at Ends of Higher Grade Construction in Line of Lower Grade 

Grade B: Pins and ties or other conductor fastenings connected to the structure at a deadend 
or at each end of the higher grade section shall be designed to withstand an unbalanced pull 
due to the conductor load in Rule 251 multiplied by the overload factors in Rule 253-1. 
Grade C: This requirement is not applicable except for deadends. 

d. At Ends of Transverse Sections Described in Rule 261 A3 

Grade B: Pins and ties or other conductor fastenings connected to the structure at ends of the 
transverse section as described in Rule 261 A3 shall be designed to withstand the unbalanced 
pull in the direction of that transverse section under the load in Rule 252 multiplied by the 
overload factors in Rule 253-1. 
Grade C: No requirement. 

2. Double Pins and Conductor Fastenings 

Grade B: Double pins and conductor fastenings shall be used where double crossarms or brackets 
are required by Rule 261D4c. 

EXCEPTION: The above does not apply where communication cables or conductors cross below supply 
conductors and either are attached to the same pole, or where supply conductors are continuous and of uni- 
form tension in a crossing span and each adjacent span. This exception does not apply in the case of railroad 
crossings and limited access highway crossings except by mutual agreement. 
Grade C: No requirement. 

3. Single Supports Used in Lieu of Double Wood Pins 

A single conductor support and its conductor fastening, when used in lieu of double wood pins, 
shall develop strength equivalent to double wood pins and their conductor fastenings as specified 
in Rule 261Fla. 

G. Armless Construction 

1. General 

Open conductor armless construction is a type of open conductor supply line construction in 
which conductors are individually supported at the structure without the use of crossarms. 

2. Insulating Material 

Strength of insulating material shall meet the requirements of Section 27. 

3. Other Components 

Strengths of other components shall meet the requirements of Rules 260 and 261. 

H. Open Supply Conductors and Overhead Shield Wires 

1. Sags and Tensions 

a. The supply conductor and overhead shield wire tensions shall be not more than 60 percent of 
their rated breaking strength for the load of Rule 250B in Rule 25 1 multiplied by an overload 
factor of 1.0. 

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261Hlb PART 2. SAFETY RULES FOR OVERHEAD LINES 261L1 



b . The tension at 1 5 °C (60 °F) , without external load , shall not exceed the following percentages 
of their rated breaking strength: 

Initial unloaded tension 35% 

Final unloaded tension 25% 

EXCEPTION: In the case of conductors with a generally triangular cross section, such as cables 
composed of three wires, the final unloaded tension at 15 °C (60 °F) shall not exceed 30% of the rated 
breaking strength of the conductor. 

NOTE: The above limitations are based on the use of recognized methods for avoiding fatigue failures 
by minimizing chafing and stress concentration. If such practices are not followed, lower tensions 
should be employed. 

2 . Splices , Taps , Dead-End Fittings , and Associated Attachment Hardware 

a. Splices should be avoided in crossings and adjacent spans. If it is impractical to avoid such 
splices, they shall have sufficient strength to withstand the maximum tension resulting from 
the loads of Rule 250B in Rule 251 multiplied by an overload factor of 1 .65. If Rule 250C is 
applicable, splices shall not be stressed beyond 80% of their rated breaking strength under the 
loads of Rule 250C in Rule 251 multiplied by an overload factor of 1.0. 

b. Taps should be avoided in crossing spans but, if required, shall be of a type that will not impair 
the strength of the conductors to which they are attached. 

c. Dead-end fittings, including the associated attachment hardware, shall have sufficient 
strength to withstand the maximum tension resulting from the loads of Rule 250B in Rule 251 
multiplied by an overload factor of 1 .65. If Rule 250C is applicable, deadend fittings shall not 
be stressed beyond 80% of their rated breaking strength under the loads of Rule 250C in 
Rule 251 multiplied by an overload factor of 1 .0. 

3. Trolley-Contact Conductors 

In order to provide for wear, no trolley-contact conductor shall be installed of less size than AWG 
No. 0, if of copper, or AWG No. 4, if of silicon bronze. 

I. Supply Cable Messengers 

Messengers shall be stranded and shall not be stressed beyond 60% of their rated breaking strength 
under the loads of Rule 250B in Rule 251 multiplied by an overload factor of 1 .0. If Rule 250C is 
applicable, messengers shall not be stressed beyond 80% of their rated breaking strength under the 
loads of Rule 250C in Rule 251 multiplied by an overload factor of 1 .0. 
NOTE: There are no strength requirements for cables supported by messengers. 

J. Open- Wire Communication Conductors 

Open-wire communication conductors in Grade B or C construction shall have the tensions and sags 
in Rule 261H1 for supply conductors of the same grade. 

EXCEPTION: Where supply conductors are trolley-contact conductors of to 750 V to ground, WG 
No. 12 Stl may be used for communication conductors for spans of to 30 m (0 to 100 ft), and Stl 
WG No. 9 may be used for spans of 38 to 45 m (125 to 150 ft). 

K. Communication Cables 

1 . Communication Cables 

There are no strength requirements for communication cables supported by messengers. See 
Rule 261K2 for the strength requirements for messengers supporting communication cables. 

2. Messenger 

The messenger shall not be stressed beyond 60% of its rated breaking strength under the loads of 
Rule 250B in Rule 25 1 multiplied by an overload factor of 1 .0. If Rule 250C is applicable, mes- 
sengers shall not be stressed beyond 80% of their rated breaking strength under the loads of Rule 
250C in Rule 251 multiplied by an overload factor of 1 .0. 

L. Paired Communication Conductors 

1 . Paired Conductors Supported on Messenger 

180 
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261Lla PART 2. SAFETY RULES FOR OVERHEAD LINES 261M 



a. Use of Messenger 

A messenger may be used for supporting paired conductors in any location, but is required for 
paired conductors crossing over trolley-contact conductors of more than 7.5 kV to ground. 

b. Sag of Messenger 

Messenger used for supporting paired conductors required to meet Grade B construction be- 
cause of crossing over trolley-contact conductors shall meet the sag requirements for Grade B . 

c. Size and Sag of Conductors 

There are no requirements for paired conductors when supported on messenger. 
2. Paired Conductors Not Supported on Messenger 

a. Above Supply Lines 

Grade B: Sizes and sags shall be not less than those in Rule 261H1 for supply conductors of 

similar grade. 

Grade C: Sizes and sags shall be not less than the following: 

Spans to 30 m (0 to 100 ft)— No sag requirements. 

Each conductor shall have a rated breaking strength of not less than 0.75 kN (170 lb). 

Spans 30 to 45 m (100 to 150 ft)— Sizes and sags shall be not less than required for Grade B 

communication conductors. 

Spans exceeding 45 m (150 ft)— Sizes and sags shall be not less than required for Grade C 

supply conductors. (See Rule 261H1). 

b. Above Trolley-Contact Conductors 

Grade B: Sizes and sags shall be not less than the following: 

Spans to 30 m (0 to 100 ft)— No size requirements. Sags shall be not less than for AWG No. 

8 hard-drawn copper. (See Rule 261 HI.) 

Spans exceeding 30 m (100 ft)— Each conductor shall have a rated breaking strength of not 

less than .75 kN ( 1 70 lb) . Sags shall be not less than for AWG No . 8 hard-drawn copper. (See 

Rule261Hl.) 

Grade C: Sizes and sags shall be as follows: 

Spans to 30 m (0 to 100 ft)— No requirements. 

Spans exceeding 30 m (100 ft)— No sag requirements. 

Each conductor shall have a rated breaking strength of not less than 0.75 kN (170 lb). 

M. Support and Attachment Hardware 

The strength required for all support and attachment hardware not covered by Rule 26 IF or Rule 
261H2 shall be not less than the load times the appropriate overload factor given in Section 25. For 
appropriate strength factors, see Rule 260B. 



I 



181 
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T-261-1A 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-261-1B 



I 



Table 261-1A 

Strength Factors for Structures, 1 Crossarms, Support Hardware, Guys, Foundations, and Anchors 

for Use with Overload Factors of Table 253-1 

[It is recognized that structures will experience some level of deterioration after installation, depending upon 
materials, maintenance, and service conditions. The table values specify strengths required at installation. 
Footnotes specify deterioration allowed, if any. When new or changed facilities add loads to existing struc- 
tures (a) the strength of the structure when new shall have been great enough to support the additional loads 
and (b) the strength of the deteriorated structure shall exceed the strength required at replacement. If either 
(a) or (b) cannot be met, the structure must be replaced, augmented, or rehabilitated.] 





Grade B 


Grade C 


Strength factors for use with loads of Rule 250B 


Metal and Prestressed-Concrete Structures 


1.0 


1.0 


Wood and Reinforced-Concrete Structures 2 ' 4 


0.65 


0.85 


Support Hardware 


1.0 


1.0 


Guy Wire 5 ' 6 


0.9 


0.9 


Guy Anchor and Foundation 6 


1.0 


1.0 


Strength factors for use with loads of Rule 250C 


Metal and Prestressed-Concrete Structures 6 


1.0 


1.0 


Wood and Reinforced-Concrete Structures 3 ' 4 


0.75 


0.75 


Support Hardware 


1.0 


1.0 


Guy Wire 5 ' 6 


0.9 


0.9 


Guy Anchor and Foundation 6 


1.0 


1.0 


1 







Includes poles. 

Wood and reinforced concrete structures shall be replaced or rehabilitated when deterioration reduces the 
structure strength to 2/3 of that required when installed. If a structure is replaced, it shall meet the strength 
required by Table 261-1 A. Rehabilitated portions of structures shall have strength greater than 2/3 of that 
required when installed. 

3 Wood and reinforced concrete structures shall be replaced or rehabilitated when deterioration reduces the 
structure strength to 3/4 of that required when installed. If a structure is replaced, it shall meet the strength 
required by Table 26 1-1 A. Rehabilitated portions of structures shall have strength greater than 3/4 of that 
required when installed. 

Where a wood or reinforced concrete structure is built for temporary service, the structure strength may 
be reduced to values as low as those permitted by footnotes (2) and (3) provided the structure strength does 
not decrease below the minimum required during the planned life of the structure. 

For guy insulator requirements, see Rule 279. 

Deterioration during service shall not reduce strength capability below the required strength. 

Table 261-1B 

Strength Factors for Structures 1 ' 2 and Crossarms for Use 

with Overload Factors of Table 253-2 

[It is recognized that structures will experience some levels of deterioration after installation, depending 

upon materials, maintenance, and service conditions. The table values specify strengths required at 

installation. Footnotes specify deterioration allowed for wood and reinforced concrete structures. When 

new or changed facilities add loads to existing structures (a) the strength of the structure when new shall 

have been great enough to support the additional loads, and (b) the strength of the deteriorated structure shall 

exceed the strength required at replacement. If either (a) or (b) cannot be met, the structure must be replaced, 

augmented, or rehabilitated.] 



Grade B 



Strength factors for use with loads of Rule 250B and Rule 250C 



Grade C 



Wood and Reinforced-Concrete Structures 
1 Includes poles. 



1.0 



1.0 



Where a wood or reinforced-concrete structure is built for temporary service, the structure strength may 
be reduced to values as low as those permitted by the at replacement overload factors in Table 253-2, foot- 
notes (2) and (3) provided the structure strength does not decrease below the minimum required during the 
planned life of the structure. 

182 
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T-261-2 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



263Ela(2) 



Table 261-2 
Dimensions of Crossarm Cross Section of Select Southern Pine and Douglas Fir 







Grades of Construction 




Grade B 


Grade C 


1.20 m or less mm: 


75 x 100 


70x95 


4 ft or less in: 3x4 


' ... 2-3/4x3-3/4 <■ 


2.45 m 


mm: 


82 x 108 


75 x 100 


8 ft : ,. ■',■.. ■■ ..',',;'-'[. ■.'■.■..■.; in: : '-;.- : : ■']■■.■ : : -34Mx44M :.':;.]■. '" ■ : 3 : x 4;. .■.':'■ ,: : 


3.0 m 


mm: 


82 x 108 


75 x 100 


10 ft ■;;'■■;' i,, : - :- : .'-.-- .'■■ in:,': ' : > |' : -. : ■.■34/4x4-l/4 : : - : j " ; ■ :'■ ■3x4 : ;,'- ■':'■ 



262. Number 262 not used in this edition. 

263. Grade N Construction 

The strength of Grade N construction need not be equal to or greater than Grade C. 

A. Poles 

Poles used for lines for which neither Grade B nor C is required shall be of initial size or guyed or 
braced to withstand expected loads, including line personnel working on them. 

B. Guys 

The general requirements for guys are covered in Rules 264 and 279A. 

C. Crossarm Strength 

Crossarms shall be securely supported by bracing, if necessary, to withstand expected loads, includ- 
ing line personnel working on them. 

NOTE: Double crossarms are generally used at crossings, unbalanced corners, and dead ends, in order to permit 
conductor fastenings at two insulators to limit the opportunity for slipping, although single crossarms might pro- 
vide sufficient strength. To secure extra strength, double crossarms are frequently used, and crossarm guys are 
sometimes used. 

D. Supply-Line Conductors 
1. Size 

Supply-line conductors shall be not smaller than the sizes listed in Table 263-1. 
RECOMMENDATION: It is recommended that these sizes for copper and steel not be used in spans longer 
than 45 m (150 ft) for the heavy-loading district, and 53 m (175 ft) for the medium- and light-loading 
districts. 



E. Service Drops 

1 . Size of Open- Wire Service Drops 
a. Not over 750 V. 

Service drops shall be as required by (1) or (2): 

(1) Spans not exceeding 45 m (150 ft) 

Sizes shall be not smaller than those in Table 263-2. 

(2) Spans exceeding 45 m (150 ft) 

Sizes shall be not smaller than 8 AWG. 

183 
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263Elb 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



T-263-1 



b. Exceeding 750 V 

Sizes of service drops of more than 750 V shall be not less than required for supply-line con- 
ductors of the same voltage. 

2. Tension of Open- Wire Service Drops 

The tension of the service drop conductors shall not exceed the strength of the conductor attach- 
ment or its support under the expected loads. 

3. Cabled Service Drops 

Service conductors may be grouped together in a cable, provided the following requirements are 
met: 

a. Size 

The size of each conductor shall be not less than required for drops of separate conductors 
(Rule 263E1). 

b. Tension of Cabled Service Drops 

The tension of the service drop conductors shall not exceed the strength of the conductor at- 
tachment or its support under the expected loads. 

F. Trolley-Contact Conductors 

In order to provide for wear, trolley-contact conductors shall be not smaller than size AWG No. 0, if 
of copper, or AWG No. 4, if of silicon bronze. 

G. Communication Conductors 

There are no specific requirements for Grade N communication line conductors or service drops. 

H. Street and Area Lighting Equipment 

The lowering rope or chain for luminaires arranged to be lowered for examination or maintenance 
shall be of a material and strength designed to withstand climatic conditions and to sustain the lumi- 
naire safely. 

I. Insulators 

The strength requirements for insulators are covered under Rules 277 and 279. 



Table 263-1 

Sizes for Grade N Supply Line Conductors 

(AWG for Copper and Aluminum, StI WG for Steel) 





Urban 


Rural 


Soft copper 


6 


8 


Medium- or hard-drawn copper 


8 


8 


Steel 


9 


9 




Spans 45 m 
(150 ft) or less 


Spans exceeding 45 m 
(150 ft) 


Stranded aluminum: 


EC 


4 


2 


ACSR 


6 


4 


ALLOY 


4 


4 


ACAR 


4 


2 



184 
Copyright © 2001 IEEE. All rights reserved. 



T-263-2 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



264D 



Table 263-2 
Sizes of Service Drops of 750 V or Less 

(Voltages of trolley-contact conductors are voltage to ground. 
AWG used for aluminum and copper wires; Stl WG used for steel wire.) 





Copper Wire 




Situation 


Soft-Drawn 


Medium- or 
Hard-Drawn 


Steel Wire 


EC 

aluminum 

wire 2 


Alone 


10 


12 


12 


4 


Concerned with communication 
conductor 


10 


12 


12 


4 


Over supply conductors of 


to 750 V 


10 


12 


12 


4 


750 V to 8.7 kV 1 


8 


10 


12 


4 


Exceeding 8.7 kV 1 


6 


8 


9 


4 


Over trolley-contact conductors 


to 750 V ac or dc 


8 


10 


12 


4 


Exceeding 750 V ac or dc 


6 


8 


9 


4 



*■ Installation of service drops of not more than 750 V above supply lines of more than 750 V should 
be avoided where practical. 
^ ACSR or high-strength aluminum alloy conductor size shall be not less than No. 6. 

264. Guying and Bracing 

A. Where Used 

When the loads are greater than can be supported by the structure alone, additional strength shall be 
provided by the use of guys, braces, or other suitable construction. Such measures shall also be used 
where necessary to limit the increase of sags in adjacent spans and provide sufficient strength for 
those supports on which the loads are sufficiently unbalanced, for example, at corners, angles, dead 
ends, large differences in span lengths, and changes of grade of construction. 

B. Strength 

Guys shall be designed to withstand the loads in Rule 252 multiplied by the overload factors in 
Table 253-1 without exceeding the permitted load. The permitted load shall be equal to the strength 
multiplied by the strength factors in Table 261-1A. For guy wires conforming to ASTM Standards, the 
minimum breaking strength value therein defined shall be the rated breaking strength required in this 
code. 



I 



C. Point of Attachment 

The guy or brace should be attached to the structure as near as is practical to the center of the con- 
ductor load to be sustained. However, on lines exceeding 8.7 kV, the location of the guy or brace may 
be adjusted to minimize the reduction of the insulation offered by nonmetallic support arms and sup- 
porting structures. 

D. Guy Fastenings 

Guys having a rated breaking strength of 9.0 kN (2000 lb) or more and that are subject to small radius 
bends should be stranded and should be protected by suitable guy thimbles or their equivalent. Any 

185 
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264D PART 2. SAFETY RULES FOR OVERHEAD LINES 264G2 



guy having a design loading of 44.5 kN (10 000 lb) or more wrapped around cedar or similar soft- 
wood poles should be protected by the use of suitable guy shims. 

Where there is a tendency for the guy to slip off the shim, guy hooks or other suitable means of 
limiting the likelihood of this action should be used. Shims are not necessary in the case of supple- 
mentary guys, such as storm guys. 

E. Guy Markers and Protection 

1 . The ground end of anchor guys exposed to pedestrian traffic shall be provided with a substantial 
and conspicuous marker. 

NOTE: Visibility of markers can be improved by the use of color or color patterns that provide contrast with 
the surroundings. 

2. Where an anchor is located in an established parking area, the guy shall either be protected from 
vehicle contact or marked. 

3. Nothing in this rule is intended to require protection or marking of structural components located 
outside of the traveled ways of roadways or established parking areas. Experience has shown that 
it is not practical to protect structures from contact by out of control vehicles operating outside of 
established traveled ways. 

F. Electrolysis 

Where anchors and rods are subject to electrolysis, suitable measures should be taken to minimize 
corrosion from this source. 

G. Anchor Rods 

1. Anchor rods should be installed so as to be in line with the pull of the attached guy when under 
load. 

EXCEPTION: This is not required for anchor rods installed in rock or concrete. 

2. The anchor and rod assembly shall have an ultimate strength not less than that required of the 
guy(s) by Rule 264B. 



186 
Copyright © 2001 IEEE. All rights reserved. 



270 PART 2. SAFETY RULES FOR OVERHEAD LINES 275A 

Section 27. 
Line Insulation 

270. Application of Rule 

These requirements apply only to open-conductor supply lines. 

NOTE 1: See Rule 243C6. 

NOTE 2: See Rule 242E for insulation requirements for neutral conductors. 

271. Material and Marking 

Insulators for operation of supply circuits shall be made of wet-process porcelain or other material that 
will provide equivalent or better electrical and mechanical performance. Insulators for use at or above 
2.3 kV between conductors shall be marked by the maker with its name or trademark and an identifi- 
cation mark or markings that will permit determination of the electrical and mechanical properties. 
The marking shall be applied so as not to reduce the electrical or mechanical strength of the insulator. 
NOTE: The identifying marking can be either a catalog number, trade number, or other means so that properties 
of the unit can be determined either through catalogs or other literature. 

272. Ratio of Flashover to Puncture Voltage 

Insulators shall be designed so that the ratio of their rated low-frequency dry-flashover voltage to low- 
frequency puncture voltage is in conformance with applicable American National Standards. When a 
standard does not exist, this ratio shall not exceed 75%. 

The applicable American National Standards are as follows: 

ANSIC29.1-1988 

ANSIC29.2-1992 

ANSI C29.3- 1986 

ANSI C29.4-1989 

ANSI C29.5-1984 

ANSI C29.6- 1996 

ANSI C29.7-1996 

EXCEPTION: Insulators specifically designed for use in areas of high atmospheric contamination may have a 
rated low-frequency dry-flashover voltage not more than 80% of their low-frequency puncture voltage. 

273. Insulation Level 

The rated dry flashover voltage of the insulator or insulators, when tested in accordance with 
ANSI C29.1-1988, shall be not less than that shown in Table 273-1, unless based on a qualified engi- 
neering study. Higher insulation levels than those shown in Table 273-1, or other effective means, 
shall be used where severe lightning, high atmospheric contamination, or other unfavorable condi- 
tions exist. Insulation levels for system voltages in excess of those shown shall be based on a qualified 
engineering study. 

274. Factory Tests 

Each insulator or insulating part thereof for use on circuits operating at or above 2.3 kV between con- 
ductors shall be tested by the manufacturer in accordance with applicable American National Standards, 
or, where such standards do not exist, other good engineering practices to ensure their performance. 
The applicable American National Standards are listed in Rule 272. 

275. Special Insulator Applications 

A. Insulators for Constant-Current Circuits 

Insulators for use on constant-current circuits shall be selected on the basis of the rated full-load volt- 
age of the supply transformer. 

187 
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T-273-1 



PART 2. SAFETY RULES FOR OVERHEAD LINES 



278A3 



Table 273-1 
Insulation Level Requirements 



Nominal voltage 
(between phases) 

(kV) 


Rated dry 

flashover voltage 

of insulators 1 

(kV) 


Nominal voltage 
(between phases) 

(kV) 


Rated dry 

flashover voltage 

of insulators l 

(kV) 


0.75 


5 


115 


315 


2.4 


20 


138 


390 


6.9 


39 


161 


445 


13.2 


55 


230 


640 


23.0 


75 


345 


830 


34.5 


100 


500 


965 


46 


125 


765 


1145 


69 


175 







1 Interpolate for intermediate values. 



B. Insulators for Single-Phase Circuits Directly Connected to Three-Phase Circuits 

Insulators used on single-phase circuits directly connected to three-phase circuits (without interven- 
ing isolating transformers) shall have an insulation level not less than that required for the three-phase 
circuit. 

| 276. Number 276 not used in this edition. 



277. Mechanical Strength of Insulators 

I Insulators shall withstand all applicable loads specified in Rules 250, 251, and 252 except those of 

Rule 250C without exceeding the following percentages of their rated ultimate strength for the spec- 
ified application: 

Cantilever 40% 

Compression 50% 
Tension 50% 

Proper allowance should be made for the loads in Rule 250C. 

I NOTE 1: The rated ultimate strength of suspension type insulators (used in tangent, angle, or dead-end applica- 

tions) is considered to be: 

a. For porcelain or toughed glass insulators, the manufacturer's "combined mechanical and electrical strength" 
as determined per ANSI C29. 1-1988. 

Ib. For composite insulators, the manufacturer' s "specified cantilever load" for cantilever or "specified mechan- 
ical load" for tension, per IEEE Std 1024-1988. 

NOTE 2: The rated ultimate strength of porcelain post insulators is considered to be the manufacturer's strength 
| rating per ANSI C29.7-1996 and ANSI C29.9- 1983 [B7]. 

278. Aerial Cable Systems 

A. Electrical Requirements 

1 . Covered or insulated conductors not meeting the requirements of Rule 230C1 , 230C2, or 230C3 
shall be considered as bare conductors for all insulation requirements. 

2. The insulators or insulating supports shall meet the requirements of Rule 273. 

3. The systems shall be so designed and installed as to minimize long-term deterioration from elec- 
trical stress. 

188 
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278B PART 2. SAFETY RULES FOR OVERHEAD LINES 279B lb 



B. Mechanical Requirements 

1. Insulators other than spacers used to support aerial cable systems shall meet the requirements of 
Rule 277. 

2. Insulating spacers used in spacer cable systems shall withstand the loads specified in Section 25 
(except those of Rule 250C) without exceeding 50% of their rated ultimate strength. 

279. Guy and Span Insulators 

A. Insulators 

1 . Properties of Guy Insulators 

a. Material 

Insulators shall be made of wet-process porcelain, wood, fiberglass-reinforced plastic, or oth- 
er material of suitable mechanical and electrical properties. 

b. Electrical Strength 

The guy insulator shall have a rated dry flashover voltage at least double, and a rated wet 
flashover voltage at least as high as, the nominal line voltage between conductors of the guyed 
circuit. A guy insulator may consist of one or more units. 

c. Mechanical Strength 

The rated ultimate strength of the guy insulator shall be at least equal to the required strength 
of the guy in which it is installed. 

2. Use of Guy Insulators 

a. Ungrounded guys shall be insulated if attached to a supporting structure carrying any supply 
| conductors of more than 300 V or if vulnerable to accidental energization by such conductors 

due to a slack conductor or guy. 

NOTE: Guys grounded in accordance with Rule 215C2 need not be insulated. 
j EXCEPTION: A guy insulator is not required if the guy is attached to a supporting structure on private 

right-of-way if all the supply circuits exceeding 300 V meet the requirements of Rule 220B2. 



I 



b. Insulators shall be installed as follows: 

(1) All insulators shall be located at a position that maintains the bottom of the insulator not 
less than 2.45 m (8 ft) above the ground if the guy is broken below the insulator. 

(2) Insulators shall be so placed that, in case any guy contacts, or is contacted by, an 
energized conductor or part, the voltage will not be transferred to other facilities on the 
structure(s). 

EXCEPTION: Guy insulators are not required if both of the following conditions are fulfilled. 

(a) The supply voltage will be promptly removed by de-energization or by other means, both ini- 
tially and following subsequent circuit breaker operations in the event of a contact. 

(b) The voltage and current impressed on the other facilities in the event of a contact are not in 
excess of the safe operating limit of the protective devices of such facility. 

(3) Insulators shall be so placed that in case any guy sags down upon another, the insulators 
will not become ineffective. 

3. Corrosion Protection 

An insulator in the guy strand used exclusively for the elimination of corrosion of metal in ground 
rods, anchors, anchor rods, or pipe in an effectively grounded system shall not be classified as a 
guy insulator and shall not reduce the mechanical strength of the guy. 

B. Span- Wire Insulators 

1 . Properties of Span- Wire Insulators 

a. Material 

Insulators shall be made of wet-process porcelain, wood, fiberglass, or other material of suit- 
able mechanical and electrical properties. 

b. Insulation Level 

The insulation level of span-wire insulators shall meet the requirements of Rule 274. 

A hanger insulator, where used to provide single insulation as permitted by Rule 279B2, 
shall meet the requirements of Rule 274. 

189 
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I 



279B lc PART 2. SAFETY RULES FOR OVERHEAD LINES 279B2b 



c. Mechanical Strength 

The rated ultimate strength of the span-wire insulator shall be at least equal to the required 
strength of the span wire in which it is located. 
2. Use of Span- Wire Insulators 

a. All span wires, including bracket span wires, shall have a suitable insulator (in addition to an 
insulated hanger if used) inserted between each point of support of the span wire and the lu- 
minaire or trolley-contact conductor supported. 

EXCEPTION 1: Single insulators, as provided by an insulated hanger, may be permitted when the span 

wire or bracket is supported on wood poles supporting only trolley, railway feeder, or communication 

conductors used in the operation of the railway concerned. 

EXCEPTION 2: Insulators are not required if the span wire is effectively grounded. 

EXCEPTION 3: This rule does not apply to insulated feeder taps used as span wires. 

b. In case insulated hangers are not used, the insulator shall be located so that in the event of a 
broken wire the energized part of the span wire cannot be reached from the ground. 

Section number 28 not used in this edition. 

Section number 29 not used in this edition. 



190 
Copyright © 2001 IEEE. All rights reserved. 



300 PART 3. SAFETY RULES FOR UNDERGROUND LINES 302 

Part 3. 

Safety Rules for the Installation and 

Maintenance of Underground Electric Supply 

and Communication Lines 

Section 30. 
Purpose, Scope, and Application of Rules 

300. Purpose 

The purpose of Part 3 of this code is the practical safeguarding of persons during the installation, op- 
eration, or maintenance of underground or buried supply and communication cables and associated 
equipment. 

301. Scope 

Part 3 of this code covers supply and communication cables and equipment in underground or buried 
systems. The rules cover the associated structural arrangements and the extension of such systems into 
buildings. It also covers the cables and equipment employed primarily for the utilization of electric 
power when such cables and equipment are used by the utility in the exercise of its function as a utility. 
They do not cover installations in electric supply stations. 

302. Application of Rules 

The general requirements for application of these rules are contained in Rule 013. 



I 



191 
Copyright © 2001 IEEE. All rights reserved. 



310 PART 3. SAFETY RULES FOR UNDERGROUND LINES 314B 



Section 31. 

General Requirements 

Applying to Underground Lines 

310. Referenced Sections 

The Introduction (Section 1), Definitions (Section 2), List of Referenced Documents (Section 3), and 
Grounding Methods (Section 9) of this code shall apply to the requirements of Part 3. 

311. Installation and Maintenance 

A. Persons responsible for underground facilities shall be able to indicate the location of their facilities. 

B. Reasonable advance notice should be given to owners or operators of other proximate facilities that 
may be adversely affected by new construction or changes in existing facilities. 

312. Accessibility 

All parts that must be examined or adjusted during operation shall be arranged so as to be readily ac- 
cessible to authorized persons by the provision of adequate working spaces, working facilities, and 
clearances. 

313. Inspection and Tests of Lines and Equipment 

A. When In Service 

1. Initial Compliance With Safety Rules 

Lines and equipment shall comply with these safety rules upon being placed in service. 

2. Inspection 

Accessible lines and equipment shall be inspected by the responsible party at such intervals as 
experience has shown to be necessary. 

3. Tests 

When considered necessary, lines and equipment shall be subjected to practical tests to determine 
required maintenance. 

4. Record of Defects 

Any defects affecting compliance with this code revealed by inspection, if not promptly correct- 
ed, shall be recorded; such record shall be maintained until the defects are corrected. 

5. Remedying Defects 

| Lines and equipment with recorded defects that would endanger life or property shall be promptly 

repaired, disconnected, or isolated. 

B. When Out of Service 

1. Lines Infrequently Used 

Lines and equipment infrequently used shall be inspected or tested as necessary before being 
placed into service. 

2. Lines Temporarily Out of Service 

Lines and equipment temporarily out of service shall be maintained in a safe condition. 

3. Lines Permanently Abandoned 

Lines and equipment permanently abandoned shall be removed or maintained in a safe condition. 

314. Grounding of Circuits and Equipment 

A. Methods 

The methods to be used for grounding of circuits and equipment are given in Section 9. 

B. Conductive Parts to Be Grounded 

Cable sheaths and shields (except conductor shields), equipment frames and cases (including pad- 
mounted devices), and conductive lighting poles shall be effectively grounded. Conductive-material 
| ducts and riser guards that enclose electric supply lines or are exposed to contact with open supply 

192 
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3 14B PART 3. SAFETY RULES FOR UNDERGROUND LINES 316 



conductors of greater than 300 V shall be effectively grounded. 

EXCEPTION: This rule does not apply to parts that are 2.45 m (8 ft) or more above readily accessible surfaces 

or are otherwise isolated or guarded. 

C. Circuits 

1. Neutrals 

Primary neutrals, secondary and service neutrals, and common neutrals shall be effectively 

grounded as specified in Rule 314A. 

EXCEPTION: Circuits designed for ground-fault detection and impedance current-limiting devices. 

2. Other Conductors 

Conductors, other than neutral conductors, that are intentionally grounded, shall be effectively 
grounded as specified in Rule 314A. 

3. Surge Arresters 

Surge arresters shall be effectively grounded as specified in Rule 314A. 

4. Use of Earth as Part of Circuit 

a. Supply circuits shall not be designed to use the earth normally as the sole conductor for any 
part of the circuit. 

b. Monopolar operation of a bipolar HVDC system is permissible for emergencies and limited 
periods for maintenance. 

315. Communications Protective Requirements 

A. Where Required 

Where communications apparatus is handled by other than qualified persons, it shall be protected by 
one or more of the means listed in Rule 315B if such apparatus is permanently connected to lines sub- 
ject to any of the following: 

1. Lightning 

2. Contact with supply conductors with voltages exceeding 300 V 

3. Transient rise in ground potential exceeding 300 V 

4. Steady-state induced voltage of a level that may cause personal injury 

NOTE: When communication cables will be in the vicinity of supply stations where large ground currents 
may flow, the effect of these currents on communication circuits should be evaluated. 

B. Means of Protection 

Where communications apparatus is required to be protected under Rule 315A, protective means ad- 
equate to withstand the voltage expected to be impressed shall be provided by insulation, protected 
where necessary by surge arresters. Severe conditions may require the use of additional devices such 
as auxiliary arresters, drainage coils, neutralizing transformers, or isolating devices. 

316. Induced Voltage 

Rules covering supply-line influence and communication-line susceptiveness have not been detailed 
in this code. Cooperative procedures are recommended to minimize steady-state voltages induced 
from proximate facilities. Therefore, reasonable advance notice should be given to owners or 
operators of other known proximate facilities that may be adversely affected by new construction or 
changes in existing facilities. 






193 
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320 PART 3. SAFETY RULES FOR UNDERGROUND LINES 320B 1 

Section 32. 
Underground Conduit Systems 

| NOTE 1: While it is often the practice to use duct and conduit interchangeably, duct, as used herein, is a single enclosed 
raceway for conductors or cable; conduit is a structure containing one or more ducts; and conduit system is the combina- 
tion of conduit, conduits, manholes, handholes, and/or vaults joined to form an integrated whole. 

| NOTE 2: For cables installed in a single duct not part of a conduit system, the rales in Section 35 apply. 

320. Location 

A. Routing 

1. General 

a. Conduit systems should be subject to the least disturbance practical. Conduit systems extend- 
ing parallel to other subsurface structures should not be located directly over or under other 
subsurface structures. If this is not practical, the rule on separation, as stated in Rule 320B, 
should be followed. 

b. Conduit alignment should be such that there are no protrusions that would be harmful to the 
cable. 

c. Where bends are required, the bending radius shall be sufficiently large to limit the likelihood 
of damage to cable being installed in the conduit. 

I 

2. Natural Hazards 

Routes through unstable soils such as mud, shifting soil, etc., or through highly corrosive soils, 
should be avoided. If construction is required in these soils, the conduit should be constructed in 
such a manner as to minimize movement or corrosion or both. 

3. Highways and Streets 
Where conduit must be installed longitudinally under the roadway, it should be installed in the 
shoulder. If this is not practical, the conduit should be installed within the limits of one lane of 
traffic. 

4. Bridges and Tunnels 
The conduit system shall be located so as to limit the likelihood of damage by traffic. It should be 
located to provide safe access for inspection or maintenance of both the structure and the conduit 
system. 

5. Crossing Railroad Tracks 

a. The top of the conduit system should be located not less than 900 mm (36 in) below the top of 
the rails of a street railway or 1.27 m (50 in) below the top of the rails of a railroad. Where 
unusual conditions exist or where proposed construction would interfere with existing instal- 
lations, a greater depth than specified above may be required. 

EXCEPTION: Where this is impractical, or for other reasons, this separation may be reduced by 
agreement between the parties concerned. In no case, however, shall the top of the conduit or any conduit 
protection extend higher than the bottom of the ballast section that is subject to working or cleaning. 

b. At crossings under railroads, manholes, handholes, and vaults should not, where practical, be 
located in the roadbed. 

6. Submarine Crossing 
Submarine crossings should be routed, installed, or both so they will be protected from erosion by 
tidal action or currents. They should not be located where ships normally anchor. 

B. Separation From Other Underground Installations 
1. General 

The separation between a conduit system and other underground structures paralleling it should 
be as large as necessary to permit maintenance of the system without damage to the paralleling 
structures. A conduit that crosses over another subsurface structure shall have a separation suffi- 
cient to limit the likelihood of damage to either structure. These separations should be determined 
by the parties involved. 

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320B 1 PART 3. SAFETY RULES FOR UNDERGROUND LINES 322A4 



EXCEPTION: When conduit crosses a manhole, vault, or subway tunnel roof, it may be supported directly 
on the roof with the concurrence of all parties involved. 

2. Separations Between Supply and Communication Conduit Systems 

Conduit systems to be occupied by communication conductors shall be separated from conduit 
systems to be used for supply systems by 

a. 75 mm (3 in) of concrete 

b. 100 mm (4 in) of masonry 

c. 300 mm ( 1 2 in) of well-tamped earth 

EXCEPTION: Lesser separations may be used where the parties concur. 

3. Sewers, Sanitary and Storm 

a. If conditions require a conduit to be installed parallel to and directly over a sanitary or storm 
sewer, it may be done provided both parties are in agreement as to the method. 

b. Where a conduit run crosses a sewer, it shall be designed to have suitable support on each side 
of the sewer to limit the likelihood of transferring any direct load onto the sewer. 

4. Water Lines 

Conduit should be installed as far as is practical from a water main in order to protect it from being 
undermined if the main breaks. Conduit that crosses over a water main shall be designed to have 
suitable support on each side as required to limit the likelihood of transferring any direct loads 
onto the main. 

5. Gas and Other Fuel Lines 

Conduit should have sufficient separation from gas and other fuel lines to permit the use of pipe 
maintenance equipment. Conduit shall not enter the same manhole, handhole, or vault with gas or 
other fuel lines. 

6. Steam Lines 

Conduit should be installed so as to limit the likelihood of detrimental heat transfer between the 
steam and conduit systems. 

321. Excavation and Backfill 

A. Trench 

The bottom of the trench should be undisturbed, tamped, or relatively smooth earth. Where the exca- 
vation is in rock, the conduit should be laid on a protective layer of clean tamped backfill. 

B. Quality of Backfill 

All backfill should be free of materials that may damage the conduit system. 

RECOMMENDATION: Backfill within 150 mm (6 in) of the conduit should be free of solid material greater than 
100 mm (4 in) in maximum dimension or with sharp edges likely to damage it. The balance of backfill should be 
free of solid material greater than 200 mm (8 in) in maximum dimension. Backfill material should be adequately 
compacted. 

322. Ducts and Joints 

A. General 

1. Duct material shall be corrosion-resistant and suitable for the intended environment. 

2. Duct materials, the construction of the conduit, or both shall be designed so that a cable fault in 
one duct would not damage the conduit to such an extent that it would cause damage to cables in 
adjacent ducts. 

3. The conduit system shall be designed to withstand external forces to which it may be subjected by 
the surface loadings set forth in Rule 323A, except that impact loading may be reduced one third 
for each 300 mm (12 in) of cover so no impact loading need be considered when cover is 900 mm 
(3 ft) or more. 

4. The internal surface of the duct shall be free of sharp edges or burrs, which could damage supply 
cable. 

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m\ 



322B PART 3. SAFETY RULES FOR UNDERGROUND LINES 323A5 



B. Installation 

1. Restraint 

Conduit, including terminations and bends, should be suitably restrained by backfill, concrete 
envelope, anchors, or other means to maintain its design position under stress of installation 
procedures, cable pulling operations, and other conditions such as settling and hydraulic or frost 
uplift. 

2. Joints 

Ducts shall be joined in a manner so as to limit solid matter from entering the conduit line. Joints 
shall form a sufficiently continuous smooth interior surface between joining duct sections so that 
supply cable will not be damaged when pulled past the joint. 

3. Externally Coated Pipe 

When conditions are such that externally coated pipe is required, the coating shall be corrosion 
resistant and should be inspected, tested, or both, to see that the coating is continuous and intact 
prior to backfill. Precautions shall be taken to prevent damage to the coating when backfilling. 

4. Building Walls 

Conduit installed through a building wall shall have internal and external seals intended to limit 
the likelihood of the entrance of gas into the building. The use of seals may be supplemented by 
gas- venting devices in order to minimize building up of positive gas pressures in the conduit. 

5. Bridges 

a. Conduit installed in bridges shall include the capability to allow for expansion and contraction 
of the bridge. 

b. Conduits passing through a bridge abutment should be installed so as to avoid or resist any 
shear due to soil settlement. 

c. Conduit of conductive material installed on bridges shall be effectively grounded. 

6. In Vicinity of Manholes 

Conduit should be installed on compacted soil or otherwise supported when entering a manhole 
to limit the likelihood of detrimental shear stress on the conduit at the point of manhole entrance. 

323. Manholes, Handholes, and Vaults 

A. Strength 

Manholes, handholes, and vaults shall be designed to sustain all expected loads that may be imposed 
upon the structure. The horizontal design loads, vertical design loads, or both shall consist of dead 
load, live load, equipment load, impact, load due to water table, frost, and any other load expected to 
be imposed upon the structure, to occur adjacent to the structure, or both. The structure shall sustain 
the combination of vertical and lateral loading that produces the maximum shear and bending mo- 
ments in the structure. 

1 . In roadway areas, the live load shall consist of the weight of a moving tractor-semitrailer truck 
illustrated in Fig 323-1. The vehicle wheel load shall be considered applied to an area as indicated 
in Fig 323-2. In the case of multilane pavements, the structure shall sustain the combination of 
loadings that results in vertical and lateral structure loadings that produce the maximum shear and 
bending moments in the structure. 

NOTE: Loads imposed by equipment used in road construction may exceed loads to which the completed 
road may be subjected. 

2. In designing structures not subject to vehicular loading, the design live load shall be not less than 
14.5 kPa (300 lb/ft 2 ). 

3. Live loads shall be increased by 30% for impact. 

4. When hydraulic, frost, or other uplift will be encountered, the structure shall either be of sufficient 
weight or so restrained as to withstand this force. The weight of equipment installed in the struc- 
ture is not to be considered as part of the structure weight. 

5. Where pulling iron facilities are furnished, they should be installed to withstand twice the expect- 
ed load to be applied to the pulling iron. 

196 
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F-323-1 



PART 3. SAFETY RULES FOR UNDERGROUND LINES 



F-323-2 




o 
o 
o 


O 
O 
O 


CD 


CD 



r - z 




z 

C\l 




















V 




If 





1.80m 
(6 ft) 



V = Variable spacing, 4.3 m to 9.0 m (14 ft to 30 ft), inclusive. Spacing to be used is that which results in vertical and 
lateral structure loading that produces the maximum shear and bending moments in the structure. 

Fig 323-1 
Roadway Vehicle Load 



71 .2 kN (16 000 lb) 



i 



I 



250 mm 
(10 in) 



^ 600 mm- 

(24 in) 

Fig 323-2 
Wheel Load Area 



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323B PART 3. SAFETY RULES FOR UNDERGROUND LINES 323E3 



B. Dimensions 

Manholes shall meet the following requirements: A clear working space sufficient for performing the 
necessary work shall be maintained. The horizontal dimensions of the clear working space shall be not 
less than 900 mm (3 ft). The vertical dimensions shall be not less than 1.83 m (6 ft) except in manholes 
where the opening is within 300 mm (1 ft), horizontally, of the adjacent interior side wall of the man- 
hole. 

EXCEPTION 1 : Where one boundary of the working space is an unoccupied wall and the opposite boundary con- 
sists of cables only, the horizontal working space between these boundaries may be reduced to 750 mm (30 in). 
EXCEPTION 2: In manholes containing only communication cables, equipment, or both, one horizontal dimen- 
sion of the working space may be reduced to not less than 600 mm (2 ft), provided the other horizontal dimension 
is increased so that the sum of the two dimensions is at least 1 .83 m (6 ft). 

C. Manhole Access 

1. Round access openings in a manhole containing supply cables shall be not less than 650 mm 
(26 in) in diameter. Round access openings in any manhole containing communication cables 
only, or manholes containing supply cables and having a fixed ladder that does not obstruct the 
opening, shall be not less than 600 mm (24 in) in diameter. Rectangular access openings should 
have dimensions not less than 650 mm x 560 mm (26 in x 22 in). 

2. Openings shall be free of protrusions that will injure personnel or prevent quick egress. 

3. Manhole openings shall be located so that safe access can be provided. When in the highway, they 
should be located outside of the paved roadway when practical. They should be located outside 
the area of street intersections and crosswalks whenever practical to reduce the traffic hazards to 
the workers at these locations. 

4. Personnel access openings should be located so that they are not directly over the cable or equip- 
ment. When these openings interfere with curbs, etc., they can be located over the cable if one of 
the following is provided: 

a. A conspicuous safety sign 

NOTE: ANSI Z535. 1-1998, ANSI Z535.2-1998, ANSI Z535.3-1998, ANSI Z535.4-1998, and ANSI 
Z535.5-1998 contain information regarding safety signs. 

b. A protective barrier over the cable 

c. A fixed ladder 

5. Any manhole greater than 1.25 m (4 ft) in depth shall be designed so it can be entered by means 
of a ladder or other suitable climbing device. Equipment, cable, and hangers are not suitable 
climbing devices. 

D. Covers 

1. Manholes and handholes, when not being worked in, shall be securely closed by covers of suffi- 
cient weight or proper design so they cannot be easily removed without tools. 

2. Covers should be suitably designed or restrained so that they cannot fall into manholes or protrude 
into manholes sufficiently far to contact cable or equipment. 

3. Strength of covers and their supporting structure shall be at least sufficient to sustain the applica- 
ble loads of Rule 323A. 

E. Vault and Utility Tunnel Access 

1. Access openings shall be located so that safe access can be provided. 

2. Personnel access openings in vaults should be located so that they are not directly over or do not 
directly open into equipment or cable. In vaults, other types of openings (not personnel access) 
may be located over equipment to facilitate work on, replacement, or installation of equipment. 

3. Where accessible to the public, access doors to utility tunnels and vaults shall be locked unless 
qualified persons are in attendance to restrict entry by unqualified persons. When vaults and utility 
tunnels contain exposed live parts, a prominent safety sign shall be visibly posted before entering 
the vault. 

NOTE: ANSI Z535.1-1998, ANSI Z535.2-1998, ANSI Z535.3-1998, ANSI Z535.4-1998, and ANSI 
Z535.5-1998 contain information regarding safety signs. 

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323E4 PART 3. SAFETY RULES FOR UNDERGROUND LINES 323J 



4. Such doors shall be designed so that a person on the inside may exit when the door is locked from 
the outside. 

EXCEPTION: This rule does not apply where the only means of locking is by padlock and the latching sys- 
tem is so arranged that the padlock can be closed on the latching system to prevent locking from the outside. 

F. Ladder Requirements 

Fixed ladders shall be corrosion-resistant. Portable ladders shall be used in accordance with 
Rule 420J. 

RECOMMENDATION: Ladders should conform to ANSI A14.1-1994 [Bl], ANSI A14.2-1990 [B2], ANSI 
A14.3-1992 [B3], or ANSI A14.5-1992 [B4], 

G. Drainage 

Where drainage is into sewers, suitable traps or other means should be provided to limit the likelihood 
of sewer gas entering into manholes, vaults, or tunnels. 

H. Ventilation 

Adequate ventilation to open air shall be provided for manholes, vaults, and tunnels, having an 

opening into enclosed areas used by the public. Where such enclosures house transformers, switches, 

regulators, etc., the ventilating system shall be cleaned at necessary intervals. 

EXCEPTION: This does not apply to enclosed areas under water or in other locations where it is impractical to 

comply. 

I. Mechanical Protection 

Supply cables and equipment should be installed or guarded in such a manner as to avoid damage by 
objects falling or being pushed through the grating. 

J. Identification 

Manhole and handhole covers should have an identifying mark that will indicate ownership or type of 
utility. 



I 



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■Hi 
•v ■-'"'« 



330 PART 3. SAFETY RULES FOR UNDERGROUND LINES 333D 

Section 33. 
Supply Cable 

330. General 

RECOMMENDATION: Cable should be capable of withstanding tests applied in accordance with an applicable 
standard issued by a recognized organization such as the American National Standards Institute (ANSI), the 
Association of Edison Illuminating Companies (AEIC), the Insulated Cable Engineers Association (ICEA), the 
National Electrical Manufacturers Association (NEMA), or the American Society for Testing and 
Materials (ASTM). 

A. The design and construction of conductors, insulation, sheath, jacket, and shielding shall include con- 
sideration of mechanical, thermal, environmental, and electrical stresses that are expected during in- 
stallation and operation. 

B. Cable shall be designed and manufactured to retain specified dimensions and structural integrity dur- 
ing manufacture, reeling, storage, handling, and installation. 

C. Cable shall be designed and constructed in such a manner that each component is protected from 
harmful effects of other components. 

D. The conductor, insulation, and shielding shall be designed to withstand the effects of the expected 
magnitude and duration of fault current, except in the immediate vicinity of the fault. 

331. Sheaths and Jackets 

Sheaths, jackets, or both shall be provided when necessary to protect the insulation or shielding from 
moisture or other adverse environmental conditions. 

332. Shielding 

A. General 

1. Conductor shielding should, and insulation shielding shall, be provided as specified by an appli- 
cable document issued by a nationally recognized cable standardization organization. 

NOTE: Typical cable standardization organizations include: the AEIC, the ICEA, and the NEMA. 
EXCEPTION: Shielding is not required for short jumpers that do not contact a grounded surface within en- 
closures or vaults, provided the jumpers are guarded or isolated. 

2. Insulation shielding may be sectionalized provided that each section is effectively grounded. 

B. Material 

1. The shielding system may consist of semiconducting materials, nonmagnetic metal, or both. The 
shielding adjacent to the insulation shall be designed to remain in intimate contact with the insu- 
lation under all operating conditions. 

2. Shielding material shall either be designed to resist excessive corrosion under the expected oper- 
ating conditions or shall be protected. 

333. Cable Accessories and Joints 

A. Cable accessories and joints shall be designed to withstand the mechanical, thermal, environmental, 
and electrical stresses expected during operation. 

B. Cable accessories and joints shall be designed and constructed in such a manner that each component 
of the cable and joint is protected from harmful effects of the other components. 

C. Cable accessories and joints shall be designed and constructed to maintain the structural integrity of 
the cables to which they are applied and to withstand the magnitude and duration of the fault current 
expected during operation, except in the immediate vicinity of the fault. 

D. For insulating joints, see Rule 332A2. 



200 
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340 PART 3. SAFETY RULES FOR UNDERGROUND LINES 341B2b(5) 

Section 34. 
Cable in Underground Structures 

340. General 

A. Section 33 shall apply to supply cable in underground structures. 

B. On systems operating above 2 kV to ground, the design of the conductors or cables installed in non- 
metallic conduit should consider the need for an effectively grounded shield, a sheath, or both. 

341. Installation 

A. General 

1. Bending of the supply cable during handling, installation, and operation shall be controlled to 
avoid damage. 

2. Pulling tensions and sidewall pressures on the supply cable should be limited to avoid damage. 
NOTE: Manufacturers' recommendations may be used as a guide. 

3. Ducts should be cleaned of foreign material that could damage the supply cable during pulling 
operations. 

4. Cable lubricants shall not be detrimental to cable or conduit systems. 

5. On slopes or vertical runs, consideration should be given to restraining cables to limit the likeli- 
hood of downhill movement. 

6. Supply cables shall not be installed in the same duct with communication cables unless all of the 
cables are operated and maintained by the same utility. 

7. Communication cables may be installed together in the same duct provided all utilities involved 
are in agreement. 

B. Cable in Manholes and Vaults 

1. Supports 

a. Cable supports shall be designed to withstand both live and static loading and should be com- 
patible with the environment. 

b. Supports shall be provided to maintain specified clearance between cables. 

c. Horizontal runs of supply cables shall be supported at least 75 mm (3 in) above the floor, or 
shall be suitably protected. 
EXCEPTION: This rule does not apply to grounding or bonding conductors. 

d. The installation should allow cable movement without destructive concentration of stresses. 
The cable should remain on supports during operation. 
NOTE: Special protection may be necessary at the duct entrance. 

2. Clearance 

a. Adequate working space shall be provided in accordance with Rule 323B. 

b. Between supply and communications facilities (cable, equipment, or both): 

(1) Where cable, equipment, or both are to be installed in a joint-use manhole or vault, it shall 
be done only with the concurrence of all parties concerned. 

(2) Supply and communication cables should be racked from separate walls. Crossings 
should be avoided. 

(3) Where supply and communication cables must be racked from the same wall, the supply 
cables should be racked below the communication cables. 

(4) Supply and communications facilities shall be installed to permit access to either without 
moving the other. 

(5) Clearances shall be not less than those specified in Table 341-1. 



I 



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T-341-1 



PART 3. SAFETY RULES FOR UNDERGROUND LINES 



344A2 



Table 341-1 

Clearance Between Supply and Communications Facilities 

in Joint-Use Manholes and Vaults 



Phase-to-phase supply voltage 


Surface to surface 


(mm) '■:■.. ; .'(in).-- ■■'.'■. 


to 15 000 


150 |- :■■'-., '■'.' 6 ■'"■■,' ■' 


15 001 to 50 000 


230 


9 

':,;';' : : '. 12 >;'.'■:■:' 
:■.:'.'..'. 24'. :':':" ■ 


50 001 to 120 000 


300 


120 001 and above 


600 



EXCEPTION 1: These clearances do not apply to grounding conductors. 

EXCEPTION 2: These clearances may be reduced by mutual agreement between the parties 

concerned when suitable barriers or guards are installed. 

3. Identification 

a. General 

(1) Cables shall be permanently identified by tags or otherwise at each manhole or other ac- 
cess opening of the conduit system. 

EXCEPTION: This requirement does not apply where the position of a cable, in conjunction with 
diagrams or maps supplied to workers, gives sufficient identification. 

(2) All identification shall be of a corrosion-resistant material suitable for the environment. 

(3) All identification shall be of such quality and located so as to be readable with auxiliary 
lighting. 

b. Joint-Use Manholes and Vaults 

Cables in a manhole or vault that are operated and maintained by different utilities shall be 
permanently identified by markings or tags denoting the utility name and type of cable use. 

342. Grounding and Bonding 

A. Insulation shielding of cable and joints shall be effectively grounded. 

B. Cable sheaths or shields that are connected to ground at a manhole shall be bonded or connected to a 
common ground. 

C. Bonding and grounding leads shall be of a corrosion-resistant material suitable for the environment 
or suitably protected. 

343. Fireproofing 

Although fireproofing is not a requirement, it may be provided in accordance with each utility's nor- 
mal service reliability practice to provide protection from external fire. 

344. Communication Cables Containing Special Supply Circuits 

| A. Special circuits operating at voltages in excess of 90 V ac or 150 V dc and used for supplying power 
solely to communications equipment may be included in communication cables under the following 
conditions: 

1. Such cables shall have a conductive sheath or shield that shall be effectively grounded and each 
such circuit shall be carried on conductors that are individually enclosed with an effectively 
grounded shield. 

2. All circuits in such cables shall be owned or operated by one party and shall be maintained only 
by qualified personnel. 



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344A3 PART 3. SAFETY RULES FOR UNDERGROUND LINES 344A6 



3. Supply circuits included in such cables shall be terminated at points accessible only to qualified 
employees. 

4. Communication circuits brought out of such cables, if they do not terminate in a repeater station 
or terminal office, shall be protected or arranged so that in event of a failure within the cable, the 
voltage on the communication circuit will not exceed 400 V to ground. 

5. Terminal apparatus for the power supply shall be so arranged that live parts are inaccessible when 
such supply circuits are energized. 

6. Such cables shall be identified, and the identification shall meet the pertinent requirements of 
Rule 341B3. 

EXCEPTION: The requirements of Rule 344A do not apply to communication circuits where the transmitted 
power does not exceed 150 W. 



I 



203 
Copyright © 2001 IEEE. All rights reserved. 



350 PART 3. SAFETY RULES FOR UNDERGROUND LINES 351A4 



Section 35. 
Direct-Buried Cable 

350. General 

A. Section 33 shall apply to direct-buried supply cable. 

B. Cables operating above 600 V to ground shall have a continuous metallic shield, sheath, or concentric 
neutral that is effectively grounded. 

EXCEPTION: At a splice or joint, the current path of the metallic shield, sheath, or neutral shall be made contin- 
uous but need not be concentric. 

C. Cables meeting Rule 350B of the same supply circuit may be buried with no deliberate separation. 

D. Cables of the same circuit operating below 600 V to ground and without an effectively grounded 
shield or sheath shall be placed in close proximity (no intentional separation) to each other. 

E. Communication cables containing special circuits supplying power solely to communications equip- 
ment shall comply with the requirements of Rules 344A1 through 344 A5. 

F. Bonding should be provided between all above ground metallic power and communications apparatus 
(pedestals, terminals, apparatus cases, transformer cases, etc.) that are separated by a distance of 1 .8 m 
(6 ft) or less. 

G. All direct-buried jacketed supply cable meeting Rule 350B and all direct-buried communication ca- 
bles shall be legibly marked as follows: 

The appropriate identification symbol shown in Fig 350-1 shall be indented or embossed in the 
outermost cable jacket at a spacing of not more than 1 m (40 in). The symbol may be separate or 
sequentially combined with other data, or symbols, or both, printed on the jacket. If the symbol is 
sequentially combined, it shall be separated as indicated in Fig 350-1. 

This rule became effective for cable installed on or after 1 January 1996. 
EXCEPTION 1: Cables with jackets that cannot be effectively marked in accordance with Rule 350G need not 
be marked. 

EXCEPTION 2: Unmarked cable from stock existing prior to 1 January 1996 may be used to repair unmarked 
direct-buried jacketed supply cables and communication cables. 

H. The rules in this section also apply to direct-buried supply and communication cables installed in duct 
that is not part of a conduit system. 

351. Location and Routing 

A. General 

1. Cables should be located so as to be subject to the least disturbance practical. When cables are to 
be installed parallel to and directly over or under other subsurface structures, the rules on separa- 
tion in Rule 353 or 354, as applicable, shall be followed. 

2. Cables should be installed in as straight and direct a line as practical. Where bends are required, 
the bending radius shall be sufficiently large to limit the likelihood of damage to the cable being 
installed. 

3. Cable systems should be routed so as to allow safe access for construction, inspection, and 
maintenance. 

4. The location of structures in the path of the projected cable route shall, as far as practical, be de- 
termined prior to trenching, plowing, or boring operation. 



204 
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F-350-1 



PART 3. SAFETY RULES FOR UNDERGROUND LINES 



351C3b 



PRINTED 
DATA 

CLEAR 
SPACE 



h 



3H- 



-3H- 



XXXX 



£=^ 



•3H 



H 



H 



XXXX 



T 



SYMBOL FOR COMMUNICATION CABLE 



PRINTED 
DATA 



I 



CLEAR 
SPACE 



I 



[*— 3H A — 3H p — 3H — 4 



XXXX 



H 

T 



XXXX 



SYMBOL FOR SUPPLY CABLE 
H = Height of printed characters; determined by cable manufacturer 

Fig 350-1 
Symbols for Identification of Buried Cables 



B. Natural Hazards 

Routes through unstable soil such as mud, shifting soils, corrosive soils, or other natural hazards 
should be avoided. If burying is required through areas with natural hazards, the cables shall be con- 
structed and installed in such a manner as to protect them from damage. Such protective measures 
should be compatible with other installations in the area. 

C. Other Conditions 

1. Swimming Pools 

Supply cable should not be installed within 1 .5 m (5 ft) of a swimming pool or its auxiliary equip- 
ment. If 1.5 m (5 ft) is not attainable, supplemental mechanical protection shall be provided. 

2. Buildings and Other Structures 

Cable should not be installed directly under building or storage tank foundations. Where a cable 
must be installed under such a structure, the structure shall be suitably supported to limit the like- 
lihood of transfer of a detrimental load onto the cable. 

3. Railroad Tracks 

a. The installation of cable longitudinally under the ballast section for railroad tracks should be 
avoided. Where cable must be installed longitudinally under the ballast section of a railroad, 
it should be located at a depth of not less than 1.27 m (50 in) below the top of the rail. 
EXCEPTION: Where this is impractical, or for other reasons, this clearance may be reduced by agree- 
ment between the parties concerned. 

NOTE: Where unusual conditions exist or where proposed construction would interfere with existing 
installations, a greater depth than specified above would be required. 

b. Where a cable crosses under railroad tracks, the same clearances indicated in Rule 320A5 
shall apply. 



I 



205 
Copyright © 2001 IEEE. All rights reserved. 



351C4 



PART 3. SAFETY RULES FOR UNDERGROUND LINES 



T-352-1 



M 



4. Highways and Streets 

The installation of cable longitudinally under traveled surfaces of highways and streets should be 
avoided. When cable must be installed longitudinally under the roadway, it should be installed in 
the shoulder or, if this is not practical, within the limits of one lane of traffic to the extent practical. 

5. Submarine Crossings 

Submarine crossings should be routed, installed, or both, so they will be protected from erosion 
by tidal action or currents. They should not be located where ships normally anchor. 

| 352. Installation 

A. Trenching 

The bottom of the trench receiving direct-buried cable should be relatively smooth, undisturbed earth; 
well-tamped earth; or sand. When excavation is in rock or rocky soils, the cable should be laid on a 
protective layer of well-tamped backfill. Backfill within 100 mm (4 in) of the cable should be free of 
materials that may damage the cable. Backfill should be adequately compacted. Machine compaction 
should not be used within 150 mm (6 in) of the cable. 

B. Plowing 

1. Plowing in of cable in soil containing rock or other solid material should be done in such a manner 
that the solid material will not damage the cable, either during the plowing operation or afterward. 

2. The design of cable-plowing equipment and the plowing-in operation should be such that the ca- 
ble will not be damaged by bending, side-wall pressure, or excessive cable tension. 

C. Boring 

Where a cable system is to be installed by boring and the soil and surface loading conditions are such 
that solid material in the region may damage the cable, the cable shall be adequately protected. 

D. Depth of Burial 

1 . The distance between the top of a cable and the surface under which it is installed (depth of burial) 
shall be sufficient to protect the cable from damage imposed by expected surface usage. 
| 2. Burial depths as indicated in Table 352-1 are considered adequate for supply cables or conduc- 

tors, except as noted in a, b, or c following: 

a. In areas where frost conditions could damage cables, greater burial depths than indicated 
above may be desirable. 

b. Lesser depths than indicated above may be used where supplemental protection is provided. 
The supplemental protection should be sufficient to protect the cable from damage imposed 
by expected surface usage. 

c. Where the surface under which a cable is to be installed is not to final grade, the cable should 
be placed so as to meet or exceed the requirements indicated above, both at the time of instal- 
lation and subsequent thereto. 

| Table 352-1 

Supply Cable or Conductor Burial Depth 

I * (See Rule 352D) 



Voltage (Phase-to-phase) 


Depth of burial 


(mm) 


:'■.■::;: (in) ■■':,;■:■-, 


to 600 


600 


'.';.'■ -.24 ..'.;'-' '■ 


601 to 50 000 


750 


■';■/■' \':3Q- ■■■'■ ■■ 


50 001 and above 


1070 


■'..:': .42'., ■■'■ .■■ 



EXCEPTION: Where conflicts with other underground facilities exist, street and 
area lighting cables operating at not more than 150 V to ground may be buried at a 
depth not less than 450 mm (18 in). 



206 
Copyright © 2001 IEEE. All rights reserved. 



353 PART 3. SAFETY RULES FOR UNDERGROUND LINES 354C 



| 353. Deliberate Separations — Equal to or Greater than 300 mm (12 in) From Underground 
Structures or Other 

A. General 

1. These rules apply to a radial separation of supply and communication cables or conductors from 
each other and from other underground structures such as sewers, water lines, gas and other fuel 
lines, building foundations, steam lines, etc., when separation is equal to or greater than 300 mm 
(12 in). 
NOTE: For radial separation less than 300 mm (12 in) see Rule 354. 

2. The radial separation should be adequate to permit access to and maintenance of either facility to 
limit damage to the other. 

B. Crossings 

1 . Where a cable crosses under another underground structure, the structure shall be suitably support- 
) ed to limit the likelihood of transfering of a detrimental load onto the cable system. 

2. Where a cable crosses over another underground structure, the cable shall be suitably supported to 
| limit the likelihood of transfering a detrimental load onto the structure. 

3. Adequate support may be provided by installing the facilities with sufficient vertical separation. 

C. Parallel Facilities 

Where a cable system is to be installed directly over and parallel to another underground structure (or 
another underground structure installed directly over and parallel to a cable), it may be done providing 
all parties are in agreement as to the method. Adequate vertical separation shall be maintained to per- 
mit access to and maintenance of either facility without damage to the other. 

D. Thermal Protection 

Cable should be installed with sufficient separation from other underground structures, such as steam 
or cryogenic lines, to avoid thermal damage to the cable. Where it is not practical to provide adequate 
clearance, a suitable thermal barrier shall be placed between the two facilities. 

354. Random Separation — Separation Less Than 300 mm (12 in) from Underground 
Structures or Other Cables 

A. General 

1. These rules apply to a radial separation of supply and communication cables or conductors from 
each other and from other underground structures when the radial separation between them will 
be less than 300 mm (12 in). 

2. Radial separation of supply and communications cables or conductors from steam lines, gas, and 
other fuel lines shall be not less than 300 mm (12 in) and shall meet Rule 353. 

3. Supply circuits operating above 300 V to ground or 600 V between conductors shall be so con- 
structed, operated, and maintained that when faulted, they shall be promptly de-energized initially 
or following subsequent protective device operation (phase-to-ground faults for grounded circuits, 
phase-to-phase faults for ungrounded circuits). 

4. Communication cables and conductors, and supply cables and conductors buried in random 
separation may be treated as one system when considering separation from other underground 
structures or facilities. 

B. Supply Cables or Conductors 

The cables or conductors of a supply circuit and those of another supply circuit may be buried together 
at the same depth with no deliberate separation between facilities, provided all parties involved are in 
agreement. 

C. Communication Cables or Conductors 

The cables or conductors of a communication circuit and those of another communication circuit may 
be buried together and at the same depth with no deliberate separation between facilities, provided all 
parties involved are in agreement. 



207 
Copyright © 2001 IEEE. All rights reserved. 



354D PART 3. SAFETY RULES FOR UNDERGROUND LINES 354D2c 



D. Supply and Communication Cables or Conductors 

Supply cables or conductors and communication cables or conductors may be buried together at the 
same depth, with no deliberate separation between facilities, provided all parties involved are in 
agreement and the applicable rules in 354D1 are met and either Rule 354D2 or 354D3 is met. 
EXCEPTION: Entirely dielectric fiber-optic communication cables may be buried together at the same depth 
with no deliberate separation from supply cables or conductors provided all parties involved are in agreement 
and Rules 354Dla, b, c, and d are met. 

1. General 

a. Grounded supply systems shall not be operated in excess of 22 000 V to ground. 

b. Ungrounded supply systems shall not be operated in excess of 5300 V phase to phase. 

c. Cables of an ungrounded supply system operating above 300 V shall be of effectively ground- 
ed concentric shield construction. Such cables shall be maintained in close proximity to each 
other. 

d. Ungrounded supply circuits operating above 300 V between conductors and in random 
separation with communication conductors shall be equipped with a ground-fault indication 
system. 

e. Communication cables and communication service wire having metallic conductors or metal- 
lic components shall have a continuous metallic shield under the outer jacket. 
EXCEPTION: This requirement does not apply to Rule 354C. 

f. Communications-protective devices shall be adequate for the voltage and currents expected 
to be impressed on them in the event of contact with the supply conductors. 

g. Adequate bonding shall be provided between the effectively grounded supply conductor or 
conductors and the communication cable shield or sheath at intervals that should not exceed 
300 m (1000 ft). 

h. In the vicinity of supply stations where large ground currents may flow, the effect of these 
currents on communication circuits should be evaluated before communication cables are 
placed in random separation with supply cables. 

2. Grounded Bare or Semiconducting Jacketed Neutral Supply Cables 

a. A supply facility operating above 300 V to ground shall include a bare or semiconducting 
jacketed grounded conductor in continuous contact with the earth. This conductor, adequate 
for the expected magnitude and duration of the fault current that may be imposed, shall be one 
of the following: 

(1) A sheath, an insulation shield, or both 

(2) Multiple concentric conductors closely spaced circumferentially 

(3) A separate conductor in contact with the earth and in close proximity to the cable, where 
such cable or cables also have a grounded sheath or shield not necessarily in contact with 
the earth. The sheath, shield, or both, as well as the separate conductor, shall be adequate 
for the expected magnitude and duration of the fault currents that may be imposed. 
NOTE: This is applicable when a cable in nonmetallic duct is considered as a direct-buried cable 
installation and random separation is desired. 

EXCEPTION: Where buried cable passes through a short section of conduit such as under a 
roadway, the contact with earth of the grounded conductor can be omitted, provided the grounded 
conductor is continuous through the conduit. 

b. The bare conductor or conductors in contact with the earth shall be of suitable corrosion-re- 
sistant material. The conductor covered by a semiconducting jacket shall be compatible with 
the jacketing compound. 

NOTE: Experience has shown that in many geographic areas, bare concentric copper neutral conductors 
experience severe corrosion. 

c. The radial resistivity of the semiconducting jacket shall be not more than 100 £2«m and shall 
remain essentially stable in service. The radial resistivity of the jacket material is that value 
calculated from measurements on a unit length of cable, of the resistance between the concen- 

, trie neutral and a surrounding conducting medium. Radial resistivity is equal to the resistance 

of a unit length times the surface area of the jacket divided by the average thickness of the 
jacket over the neutral conductors. All dimensions are to be expressed in meters. 

208 
Copyright © 2001 IEEE. All rights reserved. 



354D3 PART 3. SAFETY RULES FOR UNDERGROUND LINES 354E3 



3. Insulating Jacketed Grounded Neutral Supply Cables 

Each phase conductor of a multi-grounded supply system operating above 300 V to ground and 
having an overall insulating jacket shall have an effectively grounded copper concentric conduc- 
tor meeting all of the following requirements: 

a. A conductance not less than one half that of the phase conductor. 

b. A conductance adequate for the expected magnitude and duration of fault current that may be 
imposed. 

c. A conductance grounded in accordance with Rule 314 except that the grounding interval re- 
quired by Rule 96C shall be not less than eight in each 1.6 km (1 mile) of the random buried 
section, not including grounds at individual services. 

4. Insulating Jacketed Grounded Neutral Supply Cables in Nonmetallic Duct 

Insulating jacketed grounded neutral supply cables meeting the rules of 354D3, when installed in 
nonmetallic duct, may be random-laid with communication cables. 
E. Supply and Communication Cables or Conductors and Non-Metallic Water and Sewer Lines 

1 . Supply cables and conductors and non-metallic water and sewer lines may be buried together with 
no deliberate separation between facilities and at the same depth, provided all parties involved are 
in agreement. 

2. Communication cables and conductors and non-metallic water and sewer lines may be buried to- 
gether with no deliberate separation between facilities and at the same depth, provided all parties 
involved are in agreement. 

3. Supply cables or conductors, communication cables or conductors, non-metallic water and sewer 
lines may be buried together with no deliberate separation between facilities and at the same 
depth, provided the applicable rules in Rule 354D are met and all parties involved are in 
agreement. 



209 
Copyright © 2001 IEEE. All rights reserved. 



360 PART 3. SAFETY RULES FOR UNDERGROUND LINES 363B 



Section 36. 
Risers 

360. General 

A. Mechanical protection for supply conductors or cables shall be provided as required by Rule 239D of 
this code. This protection should extend at least 300 mm (1 ft) below ground level. 

B. Supply conductors or cable should rise vertically from the cable trench with only such deviation as 
necessary to permit a reasonable cable-bending radius. 

C. Exposed conductive pipes or guards containing supply conductors or cables shall be grounded in ac- 
cordance with Rule 314. 

361. Installation 

A. The installation should be designed so that water does not stand in riser pipes above the frost line. 

B . Conductors or cables shall be supported in a manner designed to limit the likelihood of damage to con- 
ductors, cables, or terminals. 

C. Where conductors or cables enter the riser pipe or elbow, they shall be installed in such a manner that 
shall minimize the possibility of damage due to relative movement of the cable and pipe. 

362. Pole Risers — Additional Requirements 

A. Risers should be located on the pole in the safest available position with respect to climbing space and 
exposure to traffic damage. 

B. The number, size, and location of riser ducts or guards shall be limited to allow adequate access for 
climbing. 

363. Pad-Mounted Installations 

A. Supply conductors or cables rising from the trench to transformers, switchgear, or other equipment 
mounted on pads shall be so placed and arranged that they will not bear on the edges of holes through 
the pad nor the edges of bends or other duct work below the pad. 

B. Cable entering pad-mounted equipment shall be maintained substantially at adequate depth for the 
voltage class until it becomes protected by being directly under the pad, unless other suitable mechan- 
ical protection is provided. 



210 
Copyright © 2001 IEEE. All rights reserved. 



370 PART 3. SAFETY RULES FOR UNDERGROUND LINES 374B 

Section 37. 
Supply Cable Terminations 

370. General 

A. Cable terminations shall be designed and constructed to meet the requirements of Rule 333. 

B. Riser terminations not located within a vault, pad-mounted equipment, or similar enclosure shall be 
installed in a manner designed to ensure that the clearance specified in Parts 1 and 2 of this code are 
maintained. 

C. A cable termination shall be designed to limit the likelihood of moisture penetration into the cable 
where such penetration is detrimental to the cable. 

D. Where clearances between parts at different potentials are reduced below those adequate for the volt- 
age and BIL (basic impulse insulation level), suitable insulating barriers or fully insulated terminals 
shall be provided to meet the required equivalent clearances. 

371. Support at Terminations 

A. Cable terminations shall be installed in a manner designed to maintain their installed position. 

B. Where necessary, cable shall be supported or secured in a manner designed to limit the likelihood of 
the transfer of damaging mechanical stresses to the termination, equipment, or structure. 

372. Identification 

Suitable circuit identification shall be provided for all terminations. 

EXCEPTION: This requirement does not apply where the position of the termination, in conjunction with dia- 
grams or maps supplied to workers, gives sufficient identification. 

373. Clearances in Enclosures or Vaults 

A. Adequate electrical clearances of supply terminations shall be maintained, both between conductors 
and between conductors and ground, consistent with the type of terminator used. 

B. Where exposed live parts are in an enclosure, clearances or insulating barriers adequate for the volt- 
ages and the design BIL shall be provided. 

C. Where a termination is in a vault, uninsulated live parts are permissible provided they are guarded or 
isolated. 

374. Grounding 

A. All exposed conducting surfaces of the termination device, other than live parts and equipment to 
which it is attached, shall be effectively grounded, bonded, or both. 

B. Conductive structures supporting cable terminations shall be effectively grounded. 
EXCEPTION: Grounding, bonding, or both is not required where the above parts are isolated or guarded. 



I 



211 
Copyright © 2001 IEEE. All rights reserved. 



380 PART 3. SAFETY RULES FOR UNDERGROUND LINES 381G2 

Section 38. 
Equipment 

380. General 

A. Equipment includes: 

1. Buses, transformers, switches, etc., installed for the operation of the electric supply system 

2. Repeaters, loading coils, etc., installed for the operation of the communications system 

3. Auxiliary equipment, such as sump pumps, convenience outlets, etc., installed incidental to the 
presence of the supply or communications systems 

B. Where equipment is to be installed in a joint-use manhole, it shall be done with the concurrence of all 
parties concerned. 

C. Supporting structures, including racks, hangers, or pads and their foundations, shall be designed to 
sustain all loads and stresses expected to be imposed by the supported equipment including those 
stresses caused by its operation. 

D. Pad-mounted equipment, pedestals, and other above ground enclosures, should be located not less 
than 1 .2 m (4 ft) from fire hydrants. 

EXCEPTION: Where conditions do not permit a clearance of 1 .2 m (4 ft), a clearance of not less than 900 mm 
(3 ft) is allowed. 

381. Design 

A. The expected thermal, chemical, mechanical, and environmental conditions at the location shall be 
considered in the design of all equipment and mountings. 

B. All equipment, including auxiliary devices, shall be designed to withstand the effects of normal, 
emergency, and fault conditions expected during operation. 

C. Switches shall be provided with clear indication of contact position, and the handles or activating de- 
vices clearly marked to indicate operating directions. 

RECOMMENDATION: The handles or control mechanism of all switches throughout the system should operate 
in a like direction to open and in a uniformly different direction to close in order to minimize errors. 

D. Remotely controlled or automatic devices shall have local provisions to render remote or automatic 
controls inoperable if such operation may result in a hazard to the worker. 

E. Enclosures containing fuses and interrupter contacts shall be designed to withstand the effects of nor- 
mal, emergency, and fault conditions expected during operation. 

F. When tools are to be used to connect or disconnect energized devices, space or barriers shall be de- 
signed to provide adequate clearance from ground or between phases. 

G. Pad-Mounted and Other Above-Ground Equipment 

1. Pad-mounted and other above-ground equipment shall have an enclosure that is either locked or 
otherwise secured against unauthorized entry. 

2. Access to exposed live parts in excess of 600 V shall require two separate conscious acts. The first 
shall be the opening of a door or barrier that is locked or otherwise secured against unauthorized 
entry as required by Rule 381G1. The second act shall be either the opening of a door or the re- 
moval of a barrier. 

RECOMMENDATION: A prominent and appropriate safety sign should be visible when the first door or bar- 
rier is opened or removed. 

NOTE: ANSI Z535.1-1998, ANSI Z535.2-1998, ANSI Z535.3-1998, ANSI Z535.4-1998, and ANSI 
Z535.5-1998 contain information regarding safety signs. 

212 
Copyright © 2001 IEEE. All rights reserved. 



382 PART 3. SAFETY RULES FOR UNDERGROUND LINES 385 



382. Location in Underground Structures 

A. Equipment shall not obstruct personnel access openings in manholes or vaults, nor shall it impede 
egress by persons working in the structures containing the equipment. 

B. Equipment shall not be installed closer than 200 mm (8 in) to the back of fixed ladders and shall not 
interfere with the proper use of such ladders. 

C. Equipment should be arranged in a manhole or vault to permit installation, operation, and mainte- 
nance of all items in such structures. 

D. Switching devices that have provision for manual or electrical operation shall be operable from a safe 
position. This may be accomplished by use of portable auxiliary devices, temporarily attached. 

E. Equipment should not interfere with drainage of the structure. 

F. Equipment shall not interfere with the ability to ventilate any structure or enclosure. 

383. Installation 

A. Provisions for lifting, rolling to final position, and mounting shall be adequate for the weight of the 
device. 

B . Live parts shall be guarded or isolated to limit the likelihood of contact by persons in a normal position 
adjacent to the equipment. 

C. Operating levers, inspection facilities, and test facilities shall be visible and readily accessible when 
equipment is in final location without moving permanent connections. 

D. Live parts shall be isolated or protected from exposure to conducting liquids or other material expect- 
ed to be present in the structure containing the equipment. 

E. Operating controls of supply equipment, readily accessible to unauthorized personnel, shall be se- 
cured by bolts, locks, or seals. 

384. Grounding 

A. Cases and enclosures made of conductive material shall be effectively grounded or guarded. 

B. Guards constructed of conductive material shall be effectively grounded. 

385. Identification 

Where transformers, regulators, or other similar equipment operate in multiple, tags, diagrams, or oth- 
er suitable means shall be used to indicate that fact. 



213 
Copyright © 2001 IEEE. All rights reserved. 



390 PART 3. SAFETY RULES FOR UNDERGROUND LINES 391B3 



Section 39. 
Installation in Tunnels 

390. General 

A. The installation of supply and communications facilities in tunnels shall meet the applicable require- 
ments contained elsewhere in Part 3 of this code as supplemented or modified by this section. 

B. Where the space occupied by supply or communications facilities in a tunnel is accessible to other 
than qualified persons, or where supply conductors do not meet the requirements of Part 3 of this code 
for cable systems, the installation shall be in accordance with the applicable requirements of Part 2 of 
this code. 

C. All parties concerned must be in agreement with the design of the structure and designs proposed for 
installations within it. 

391. Environment 

A. When the tunnel is accessible to the public or when workers must enter the structure to install, operate, 
or maintain the facilities in it, the design shall provide a controlled safe environment including, where 
necessary, barriers, detectors, alarms, ventilation, pumps, and adequate safety devices for all facilities. 
Controlled safe environment shall include the following: 

1 . Design to avoid poisonous or suffocation atmosphere 

2. Design to protect persons from pressurized lines, fire, explosion, and high temperatures 

3. Design to avoid unsafe conditions due to induced voltages 

4. Design to limit the likelihood of hazards due to flooding 

5. Design to ensure egress; two directions for egress shall be provided for all points in tunnels 

6. Working space, in accordance with Rule 323B, the boundary of which shall be not less than 
600 mm (2 ft) from a vehicular operating space or from exposed moving parts of machinery 

7. Safeguards designed to protect workers from hazards due to the operation of vehicles or other ma- 
chinery in tunnels 

8. Unobstructed walkways for workers in tunnels 

B. A condition of occupancy in multiple-use tunnels by supply and communications facilities shall be 
that the design and installation of all facilities is coordinated to provide a safe environment for the 
operation of supply facilities, communications facilities, or both. Safe environment for facilities shall 
include the following: 

1. Means to protect equipment from harmful effects of humidity or temperature 

2. Means to protect equipment from harmful effects of liquids or gases 

3. Coordinated design and operation of corrosion-control systems 



214 
Copyright © 2001 IEEE. All rights reserved. 



400 PART 4. RULES FOR THE OPERATION OF ELECTRIC LINES 402 

Part 4. 

Rules for the Operation of Electric Supply 

and Communications Lines and Equipment 

Section 40. 
Purpose and Scope 

400. Purpose 

The purpose of Part 4 of this code is to provide practical work rules as one of the means of safeguard- 
ing employees and the public from injury. It is not the intent of these rules to require unreasonable 
steps to comply; however, all reasonable steps shall be taken. 

401. Scope 

Part 4 of this code covers work rules to be followed in the installation, operation, and maintenance of 
electric supply and communications systems. 

402. Referenced Sections 

The Introduction (Section 1), Definitions (Section 2), References (Section 3), and Grounding Meth- 
ods (Section 9) of this code shall apply to the requirements of Part 4. 

The standards listed in Section 3 shall be used with Part 4 where applicable. 
NOTE: After ANSI C2- 1 973 [B6] was originally approved, 30 June 1 972, the US Occupational Safety and Health 
Administration (OSHA) issued 29 CFR 1926, Subpart V [B42], applying to employee safety in construction. The 
differences between this document and the editions of the NESC through the 1993 Edition were noted in foot- 
notes to the text of Part 4. 

In 1989, OSHA published in the Federal Register [01/31/89], vol. 54, no. 19, pp. 4974 to 5024 inclusive, 
Docket S — 015 [B43], a Notice of Proposed Rulemaking to issue new regulations as 29 CFR 1910.137 and 29 
CFR 1910.269 to address the work practices to be used during the operation and maintenance of generation, 
transmission, and distribution facilities. Coordination between these OSHA proposals and the 1997 Edition of 
the NESC has been effected such that the technical content of each document is harmonized at this time to the 
extent possible with the closure of the rulemaking hearing docket. In some cases, it was thus not possible for the 
OSHA final rule published as 29 CFR 1910.137 and 29 CFR 1910.269 (as published in the Federal Register, 
[01/31/94] vol. 59, no. 20, pp. 4321 to 4477 [B44]) to address all the technical information considered in this 
revision of NESC Part 4. 



I 



215 
Copyright © 2001 IEEE. All rights reserved. 



410 PART 4. RULES FOR THE OPERATION OF ELECTRIC LINES 41 1 A4 



Section 41. 

Supply and Communications Systems — 

Rules for Employers 

410. General Requirements 

A. General 

1. The employer shall inform each employee working on or about communications equipment or 
electric supply equipment and the associated lines, of the safety rules governing the employee's 
conduct while so engaged. 

When deemed necessary, the employer shall provide a copy of such rules. 

2. The employer shall provide training to all employees who work in the vicinity of exposed ener- 
gized facilities. The training shall include applicable work rules required by this Part and other 
mandatory referenced standards or rules. The employer shall ensure that each employee has dem- 
onstrated proficiency in required tasks. The employer shall provide retraining for any employee 
who, as a result of routine observance of work practices, is not following work rules. 

3. Employers shall utilize positive procedures to secure compliance with these rules. Cases may 
arise, however, where the strict enforcement of some particular rule could seriously impede the 
safe progress of the work at hand; in such cases the employee in charge of the work to be done 
should make such temporary modification of the rules as will accomplish the work without in- 
creasing the hazard. 

4. If a difference of opinion arises with respect to the application of these rules, the decision of the 
employer or the employer's authorized agent shall be final. This decision shall not result in any 
employee performing work in a manner that is unduly hazardous to the employee or to the em- 
ployee's fellow workers. 

B. Emergency Procedures and First Aid Rules 

1 . Employees shall be informed of procedures to be followed in case of emergencies and rules for 
first aid, including approved methods of resuscitation. Copies of such procedures and rules should 
be kept in conspicuous locations in vehicles and places where the number of employees and the' 
nature of the work warrants. 

2. Employees working on communications or electric supply equipment or lines shall be regularly 
instructed in methods of first aid and emergency procedures, if their duties warrant such training. 

C. Responsibility 

1. A designated person shall be in charge of the operation of the equipment and lines and shall be 
responsible for their safe operation. 

2. If more than one person is engaged in work on or about the same equipment or line, one person 
shall be designated as in charge of the work to be performed. Where there are separate work loca- 
tions, one person may be designated at each location. 

fl 411. Protective Methods and Devices 

A. Methods 

1. Access to rotating or energized equipment shall be restricted to authorized personnel. 

2. Diagrams, showing plainly the arrangement and location of the electric supply equipment and 
lines, shall be maintained on file and shall be readily available to authorized personnel for that por- 
tion of the system for which they are responsible. 

3. Employees shall be instructed as to the character of the equipment or lines and methods to be used 
before any work is undertaken thereon. 

4. Employees should be instructed to take additional precautions to ensure their safety when condi- 
tions create unusual hazards. 



PHI 



■.ttt 



216 
Copyright © 2001 IEEE. All rights reserved. 



41 IB PART 4. RULES FOR THE OPERATION OF ELECTRIC LINES 41 1F2 



B. Devices and Equipment 

An adequate supply of protective devices and equipment, sufficient to enable employees to meet the 
requirements of the work to be undertaken, and first aid equipment and materials shall be available in 
readily accessible and, where practical, conspicuous places. 

Protective devices and equipment shall conform to the applicable standards listed in Section 3. 
NOTE: The following is a list of some common protective devices and equipment, the number and kinds of which 
will depend upon the requirements of each case: 

1. Insulating wearing apparel such as rubber gloves, rubber sleeves, and headgear 

2. Insulating shields, covers, mats, and platforms 

3. Insulating tools for handling or testing energized equipment or lines 

4. Protective goggles 

5. Person at work tags, portable danger signs, traffic cones, and flashers 

6. Line worker's body belts, lanyards, and positioning straps 

7. Fire-extinguishing equipment designed for safe use on energized parts or plainly marked that they must not 
be so used 

8. Protective grounding materials and devices 

9. Portable lighting equipment 

10. First aid equipment and materials 

C. Inspection and Testing of Protective Devices 

1. Protective devices and equipment shall be inspected or tested to ensure that they are in safe work- 
ing condition. 
, 2. Insulating gloves, sleeves, and blankets shall be inspected before use. Insulating gloves and 
sleeves shall be tested as frequently as their use requires. 

3. Line-worker's body belts, lanyards, and positioning straps and other personal equipment, whether 
furnished by employer or employee, shall be inspected to ensure that they are in safe working 
condition. 

D. Signs and Tags for Employee Safety 

Safety signs and tags required by Part 4 shall comply with the provisions of ANSI Z535. 1-1998 
through ANSI Z535.5-1998, inclusive. 

E. Identification and Location 

Means shall be provided so that identification of supply and communication lines can be determined 
before work is undertaken. Persons responsible for underground facilities shall be able to indicate the 
location of their facilities. 

F. Fall Protection 

1 . Employers shall develop, implement, and maintain an effective fall protection program applicable 
to climbing or otherwise accessing and working from elevated work locations, which shall include 
all of the following: 

a. Training, retraining, and documentation 

b. Guidance on equipment selection, inspection, care, and maintenance 

c. Considerations concerning structural design and integrity, with particular reference to anchor- 
ages and their availability 

d. Rescue plans and related training 

e. Hazard recognition 

2. The employer shall not permit employees the use of 100% leather positioning straps. 



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420 PART 4. RULES FOR THE OPERATION OF ELECTRIC LINES 420E 

Section 42. 
General Rules for Employees 

420. Personal General Precautions 

A. Rules and Emergency Methods 

1. Employees shall carefully read and study the safety rules, and may be called upon at any time to 
show their knowledge of the rules. 

2. Employees shall familiarize themselves with approved methods of first aid, rescue techniques, 
and fire extinguishment. 

B. Qualifications of Employees 

1. Employees whose duties require working on or in the vicinity of energized equipment or lines 
shall perform only those tasks for which they are trained, equipped, authorized, and so directed. 
Inexperienced employees shall: (a) work under the direction of an experienced and qualified per- 
son at the site, and (b) perform only directed tasks. 

2. If an employee is in doubt as to the safe performance of any assigned work, the employee shall 
request instructions from the employee's supervisor or person in charge. 

3. Employees who do not normally work on or in the vicinity of electric supply lines and equipment 
but whose work brings them into these areas for certain tasks shall proceed with this work only 
when authorized by a qualified person. 

C. Safeguarding Oneself and Others 

1 . Employees shall heed safety signs and signals and warn others who are in danger or in the vicinity 
of energized equipment or lines. 

2. Employees shall report promptly to the proper authority any of the following: 

a. Line or equipment defects such as abnormally sagging wires, broken insulators, broken poles, 
or lamp supports 

b. Accidentally energized objects such as conduits, light fixtures, or guys 

c. Other defects that may cause a dangerous condition 

3. Employees whose duties do not require them to approach or handle electric equipment and lines 
shall keep away from such equipment or lines and should avoid working in areas where objects 
and materials may be dropped by persons working overhead. 

4. Employees who work on or in the vicinity of energized lines shall consider all of the effects of 
their actions, taking into account their own safety as well as the safety of other employees on the 
job site, or on some other part of the affected electric system, the property of others, and the public 
in general. 

5. No employee shall approach or bring any conductive object, without a suitable insulating handle, 
closer to any exposed energized part than allowed by Rule 431 (communication) or Rule 441 
(supply), as applicable. 

6. Employees should exercise care when extending metal ropes, tapes, or wires parallel to and in the 
proximity of energized high-voltage lines because of induced voltages. When it is necessary to 
measure clearances from energized objects, only devices approved for the purpose shall be used. 

D. Energized or Unknown Conditions 

Employees shall consider electric supply equipment and lines to be energized, unless they are 
positively known to be de-energized. Before starting work, employees shall perform preliminary 
inspections or tests to determine existing conditions. Operating voltages of equipment and lines 
should be known before working on or in the vicinity of energized parts. 

E. Ungrounded Metal Parts 

Employees shall consider all ungrounded metal parts of equipment or devices such as transformer 
cases and circuit breaker housings, to be energized at the highest voltage to which they are exposed, 
unless these parts are known by test to be free from such voltage. 

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420F PART 4. RULES FOR THE OPERATION OF ELECTRIC LINES 420K5 



F. Arcing Conditions 

Employees should keep all parts of their bodies as far away as practical from switches, brushes, com- 
mutators, circuit breakers, or other parts at which arcing may occur during operation or handling. 

G. Liquid-Cell Batteries 

1 . Employees shall ascertain that battery areas are adequately ventilated before performing work. 

2. Employees should avoid smoking, using open flames, or using tools that may produce sparks in 
the vicinity of liquid-cell batteries. 

3. Employees shall use eye and skin protection when handling an electrolyte. 

4. Employees shall not handle energized parts of batteries unless necessary precautions are taken to 
avoid short circuits and electrical shocks. 

H. Tools and Protective Equipment 

Employees shall use the personal protective equipment, the protective devices, and the special tools 
provided for their work. Before starting work, these devices and tools shall be carefully inspected to 
make sure that they are in good condition. 

I. Clothing 

1 . Employees shall wear clothing suitable for the assigned task and the work environment. See Rule 
410A2. 

2. When working in the vicinity of energized lines or equipment, employees should avoid wearing 
exposed metal articles. 

J. Ladders and Supports 

1. Employees shall not support themselves, or any material or equipment, on any portion of a tree, 
pole structure, scaffold, ladder, walkway, or other elevated structure or aerial device, etc., without 
it first being determined, to the extent practical, that such support is adequately strong, in good 
condition, and properly secured in place. 

2. Portable wood ladders intended for general use shall not be painted except with a clear noncon- 
ductive coating, nor shall they be longitudinally reinforced with metal. 

3. Portable metal ladders intended for general use shall not be used when working on or in the vicin- 
ity of energized parts. 

4. If portable ladders are made partially or entirely conductive for specialized work, necessary pre- 
cautions shall be taken to ensure that their use will be restricted to the work for which they are 
intended. 

K. Fall Protection 

1. At elevated locations above 3 m (10 ft), climbers shall be attached to equipment or structures by 
a fall protection system while at the worksite, at a rest site, in aerial devices, helicopters, cable 
carts, and a boatswain's chair. 

2. Qualified climbers may be permitted to be unattached to equipment or structures while climbing, 
transferring, or transitioning across obstacles on structures. Unqualified climbers shall be attached 
while performing these activities. 

3. Fall protection equipment shall be inspected before use by the employee to ensure that the equip- 
ment is in safe working condition. 

4. Fall arrest equipment shall be attached to a suitable anchorage. 

5. The employee shall determine that all components of the fall protection system are properly 
engaged and that the employee is secure in the line-worker's body belt, harness, or any other fall 
protection system. 

NOTE: Climbers need to be aware of accidental disengagement of fall protection components. Accidental 
disengagement is the sudden, unexpected release of a positioning strap snaphook from the D-ring of the line- 
worker's body belt without the user directly manipulating the latch of the snaphook. In general, there are two 
primary reasons for this occurrence. 



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420K5a PART 4. RULES FOR THE OPERATION OF ELECTRIC LINES 420O 



a. Foreign objects may open the latch of the snaphook during normal use. It is possible for the snaphook 
to come in contact with such things as hand lines, guy wires, or other apparatus. These items may place 
pressure on the latch, causing the snaphook to separate from the D-ring without the user's knowledge. 
This could cause an accident. The worker must take care to keep the snaphooks away from any potential 
causes of release. Locking snaphooks reduce the possibility of this occurrence. 

b. Roll-out is the sudden separation of the snaphook/D-ring combination when the snaphook is twisted in 
the D-ring, but the user does not deliberately open the latch. This occurs when a twist is introduced into 
a positioning strap with a snaphook/D-ring combination that is incompatible. However, compatible 
hardware, when properly maintained, will not separate in this fashion. 

6. Snaphooks shall be dimensionally compatible with the member to which they are connected so 
as to prevent unintentional disengagement of the connection. 

NOTE: 

a. The possibility exists for some snaphooks to roll out of D-rings. Attachment of a mismatched or multiple 
snaphooks, either of the nonlocking or locking type, to a single D-ring needs to be avoided. Multiple 
locking snaphooks may be attached to a single D-ring if they have been evaluated in the combination to 
be used. Locking snaphooks reduce the potential for roll-out. 

b. Disengagement through contact of the snaphook keeper with the connected member may be prevented 
by the use of a locking snaphook. 

c. Hardware compatibility can be verified. Simply attach the snaphook to the D-ring, then roll the sna- 
phook placing the latch towards the body of the D-ring. This is similar to the action that occurs when 
the strap is twisted. If the rivet falls beyond the edge of the inside of the D-ring, placing pressure on the 
latch, the hardware is not compatible, and a roll-out potential exists. 

d. Other factors may increase the potential for accidental disengagement even if the hardware is compati- 
ble (e.g., foreign objects carried on the D-rings, condition of the snaphook, the shape of the D-ring). 

7. Snaphooks shall not be connected to each other. 

8. One hundred percent leather positioning straps shall not be used. 

9. Wire rope lanyards shall be used in operations where the lanyard is subject to being cut. Wire rope 
lanyards shall not be used in the vicinity of energized lines or equipment. 

L. Fire Extinguishers 

In fighting fires or in the vicinity of exposed energized parts of electric supply systems, employees 
shall use fire extinguishers or materials that are suitable for the purpose. If this is not possible, all 
adjacent and affected equipment should first be de-energized. 

M. Machines or Moving Parts 

Employees working on normally moving parts of remotely controlled equipment shall be protected 
against accidental starting by proper tags installed on the starting devices, or by locking or blocking 
where practical. Employees shall, before starting any work, satisfy themselves that these protective 
devices have been installed. When working or in the vicinity of automatically or remotely operated 
equipment such as circuit breakers that may operate suddenly, employees shall avoid being in a po- 
sition where they might be injured from such operation. 

N. Fuses 

When fuses must be installed or removed with one or both terminals energized, employees shall use 
special tools or gloves insulated for the voltage involved. When installing expulsion-type fuses, em- 
ployees shall wear personal eye protection and take precautions to stand clear of the exhaust path of 
the fuse barrel. 

O. Cable Reels 

Cable reels shall be securely blocked so they cannot roll or rotate accidentally. 



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420P PART 4. RULES FOR THE OPERATION OF ELECTRIC LINES 421C 



P. Street and Area Lighting 

1 . The lowering rope or chain, its supports, and fastenings shall be examined periodically. 

2. A suitable device shall be provided by which each lamp on series-lighting circuits of more than 
300 V may be safely disconnected from the circuit before the lamp is handled. 
EXCEPTION: This rule does not apply where the lamps are always worked on from suitable insulated plat- 
forms or aerial lift devices, or handled with suitable insulated tools, and treated as under full voltage of the 
circuit concerned. 

421. General Operating Routines 

A. Duties of a First-Level Supervisor or Person in Charge 
This individual shall: 

1. Adopt such precautions as are within the individual's authority to prevent accidents. 

2. See that the safety rules and operating procedures are observed by the employees under the direc- 
tion of this individual. 

3. Make all the necessary records and reports, as required. 

4. Prevent unauthorized persons from approaching places where work is being done, as far as 
practical. 

5. Prohibit the use of tools or devices unsuited to the work at hand or that have not been tested or 
inspected as required. 

B. Area Protection 

1. Areas Accessible to Vehicular and Pedestrian Traffic 

a. Before engaging in work that may endanger the public, safety signs or traffic control devices, 
or both, shall be placed conspicuously to alert approaching traffic. Where further protection 
is needed, suitable barrier guards shall be erected. Where the nature of work and traffic re- 
quires it, a person shall be stationed to warn traffic while the hazard exists. 

b. When openings or obstructions in the street, sidewalk, walkways, or on private property are 
being worked on or left unattended during the day, danger signals, such as warning signs and 
flags, shall be effectively displayed. Under these same conditions at night, warning lights shall 
be prominently displayed and excavations shall be enclosed with protective barricades. 

2. Areas Accessible to Employees Only 

a. If the work exposes energized or moving parts that are normally protected, safety signs shall 
be displayed. Suitable barricades shall be erected to restrict other personnel from entering the 
area. 

b. When working in one section where there is a multiplicity of such sections, such as one panel 
of a switchboard, one compartment of several, or one portion of a substation, employees shall 
mark the work area conspicuously and place barriers to prevent accidental contact with ener- 
gized parts in that section or adjacent sections. 

3. Locations With Crossed or Fallen Wires 

An employee, finding crossed or fallen wires that are creating, or may create, a hazard, shall re- 
main on guard or adopt other adequate means to prevent accidents. The proper authority shall be 
notified. If the employee is qualified, and can observe the rules for safely handling energized parts 
by the use of insulating equipment, this employee may correct the condition. 

C. Escort 

Persons accompanying nonqualified employees or visitors or in the vicinity of electric equipment or 
lines shall be qualified to safeguard the people in their care, and see that the safety rules are observed. 



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SSH&i 



422 PART 4. RULES FOR THE OPERATION OF ELECTRIC LINES 423B4 



422. Overhead Line Operating Procedures 

Employees working on or with overhead lines shall observe the following rules in addition to appli- 
cable rules contained elsewhere in Sections 43 and 44. 

A. Setting, Moving, or Removing Poles In or Near Energized Electric Supply Lines 

1 . When setting, moving, or removing poles in or in the vicinity of energized lines, precautions shall 
be taken to avoid direct contact of the pole with the energized conductors. Employees shall wear 
suitable insulating gloves or use other suitable means where voltages may exceed rating of gloves 
in handling poles where conductors energized at potentials above 750 V can be contacted. Em- 
ployees performing such work shall not contact the pole with uninsulated parts of their bodies. 

2. Contact with trucks, or other equipment that is not bonded to an effective ground being used to 
set, move, or remove poles in or in the vicinity of energized lines shall be avoided by employees 
standing on the ground or in contact with grounded objects unless employees are wearing suitable 
protective equipment. 

B. Checking Structures Before Climbing 

1. Before climbing poles, ladders, scaffolds, or other elevated structures, employees shall deter- 
mine, to the extent practical, that the structures are capable of sustaining the additional or unbal- 
anced stresses to which they will be subjected. 

2. Where there are indications that poles and structures may be unsafe for climbing, they shall not 
be climbed until made safe by guying, bracing, or other means. 

C. Installing and Removing Wires or Cables 

1 . Precautions shall be taken to prevent wires or cables that are being installed or removed from con- 
tacting energized wires or equipment. Wires or cables that are not bonded to an effective ground 
and which are being installed or removed in the vicinity of energized conductors shall be consid- 
ered as being energized. 

2. Sag of wire or cables being installed or removed shall be controlled to prevent danger to pedes- 
trian and vehicular traffic. 

3. Before installing or removing wires or cables, the strains to which poles and structures will be 
subjected shall be considered and necessary action taken to prevent failure of supporting struc- 
tures. 

4. Employees should avoid contact with moving winch lines, especially in the vicinity of sheaves, 
blocks, and take-up drums. 

5. Employees working on or in the vicinity of equipment or lines exposed to voltages higher than 
those guarded against by the safety appliances provided shall take steps to be assured that the 
equipment or lines on which the employees are working are free from dangerous leakage or in- 
duction or have been effectively grounded. 

423. Underground Line Operating Procedures 

Employees working on or with underground lines shall observe the following rules in addition to ap- 
plicable rules contained elsewhere in Sections 43 and 44. 

A. Guarding Manhole and Street Openings 

When covers of manholes, handholes, or vaults are removed, the opening shall be promptly protected 
with a barrier, temporary cover, or other suitable guard. 

B. Testing for Gas in Manholes and Unventilated Vaults 

1 . The atmosphere shall be tested for combustible or flammable gas(es) before entry. 

2. Where combustible or flammable gas(es) are detected, the work area shall be ventilated and made 
safe before entry. 

3. Unless forced continuous ventilation is provided, a test shall also be made for oxygen deficiency. 

4. Provision shall be made for an adequate continuous supply of air. 

NOTE: The term adequate includes evaluation of both the quantity and quality of the air. 



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423C PART 4. RULES FOR THE OPERATION OF ELECTRIC LINES 423F 



C. Flames 

1. Employees shall not smoke in manholes. 

2. Where open flames must be used in manholes or vaults, extra precautions shall be taken to ensure 
adequate ventilation. 

3. Before using open flames in an excavation in areas where combustible gases or liquids may be 
present, such as in the vicinity of gasoline service stations, the atmosphere of the excavation shall 
be tested and found safe or cleared of the combustible gases or liquids. 

4. When a torch or open flame is used (as in heat shrink splicing) in proximity to a visibly exposed 
gas or other fuel line(s), adequate air space or a barrier shall be provided to protect the gas or fuel 
line(s) from the heat source. 

D. Excavation 

1 . Cables and other buried utilities in the immediate vicinity shall be located, to the extent practical, 
prior to excavating. 

2. Hand tools used for excavating in the vicinity of energized supply cables shall be equipped with 
handles made of nonconductive material. 

3. Mechanized equipment should not be used to excavate in close proximity to cables and other bur- 
ied utilities. 

4. If a gas or fuel line is broken or damaged, employees shall: 

a. Leave the excavation open 

b. Extinguish flames that could ignite the escaping gas or fuel 

c. Notify the proper authority 

d. Keep the public away until the condition is under control 

5. When a worker is required to perform tasks in trenches or excavations where a cave-in hazard ex- 
ists or the trench or excavation is in excess of 1 .5 m (5 ft) in depth, shoring, sloping, or shielding 
methods shall be used to provide employee protection. 

E. Identification 

1 . When underground facilities are exposed, they should be identified and shall be protected as nec- 
essary to avoid damage. 

2. Where multiple cables exist in an excavation, cables other than the one being worked on shall be 
protected as necessary. 

3. Before cutting into a cable or opening a splice, the cable should be identified and verified to be 
the proper cable. 

4. When multiple cables exist in an excavation, the cable to be worked on shall be positively 
identified. 

F. Operation of Power-Driven Equipment 

Employees should avoid being in manholes where power-driven rodding equipment is in operation. 



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430 PART 4. RULES FOR THE OPERATION OF ELECTRIC LINES 434 

Section 43. 
Additional Rules for Communications Employees 

430. General 

Communications employees shall observe the following rules in addition to the rules contained in 
Section 42. 

431. Approach to Energized Conductors or Parts 

A. No employee shall approach, or bring any conductive object, within the distances to any exposed en- 
ergized part as listed in Table 431-1. When repairing storm damage to communication lines that are 
joint use with electric supply lines at that or another point, employees shall: 

1. Treat all such supply and communication lines as energized to the highest voltage to which they 
are exposed, or 

2. Assure that the supply lines involved are de-energized and grounded in accordance with Section 
44. 

B. Altitude Correction 

The distances in Tables 431-1 shall be used at elevations below 900 m (3000 ft). Altitude correction 
factors as indicated in Table 441-5 shall be applied above that altitude. Altitude correction factors 
shall be applied only to the electrical component of the minimum approach distance. 

432. Joint-Use Structures 

When working on jointly used poles or structures, employees shall not approach closer than distances 
specified in Table 43 1 - 1 and shall not position themselves above the level of the lowest electric supply 
conductor exclusive of vertical runs and street lighting. 

EXCEPTION: This rule does not apply where communications facilities are attached above electric supply con- 
ductors if a rigid fixed barrier has been installed between the supply and communications facilities. 

433. Attendant on Surface at Joint-Use Manhole 

While personnel are in a joint-use manhole, an employee shall be available on the surface in the im- 
mediate vicinity to render assistance as may be required. 

434. Sheath Continuity 

Metallic or semiconductive sheath continuity shall be maintained by bonding across the opening, or 
by equivalent means, when working on buried cable or on cable in manholes. 



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T-431-1 



PART 4. RULES FOR THE OPERATION OF ELECTRIC LINES 



T-431-1 



Table 431-1 
Overhead Supply Lines and Equipment Minimum Approach Distances to Exposed Energized Parts 

(See Rule 431 in its entirety) 





Distance to Employee 


Voltage range 
(phase-to-phase, rms) 1 


Phase-to-ground 
(m) 


Phase-to-ground 

(ft-in) 


V to 50 V 2 


not specified 


net specified 


51 V to 300 V 2 


avoid contact 


avoid contact 


301 V to 750 V 2 


0.31 


1-0 


751 Vtol5kV 


0.65 


2-2 


15.1 kV to 36.0 kV 


0.91 


3-0 


36.1 kV to 46.0 kV 


1.06 


3-6 


46.1kVtol21.0kV 


1.21 


4-0 


121 kV to 140.0 kV 


1.38 


4-6 



For single-phase lines off three-phase systems, use the phase-to-phase voltage of that system. 
For single-phase systems, use the highest voltage available. 



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440 



PART 4. RULES FOR THE OPERATION OF ELECTRIC LINES 



441A3d 



Section 44. 
Additional Rules for Supply Employees 

440. General 

Supply employees shall observe the following rules in addition to the rules contained in Section 42. 

441. Energized Conductors or Parts 

Employees shall not approach, or knowingly permit others to approach, any exposed ungrounded part 
normally energized except as permitted by this rule. 

| A. Minimum Approach Distance to Live Parts 

1 . General 

Employees shall not approach or bring any conductive object within the distances to exposed parts 
that operate at the voltages listed in Table 441-1 or Table 441-4 unless one of the following is met: 
| a. The line or part is de-energized and grounded per Rule 444D. 

b. The employee is insulated from the energized line or part. Electrical protective equipment in- 
sulated for the voltage involved, such as tools, gloves, rubber gloves, or rubber gloves with 
sleeves, shall be considered effective insulation for the employee from the energized part be- 
ing worked on. 

c. The energized line or part is insulated from the employee and from any other line or part at a 
different potential. 

2. Precautions for Approach— Voltages from 51 V to 300 V 

Employees shall not contact exposed energized parts operating at 51 V to 300 V, unless the pro- 
visions of Rule 441 Al are met. 

3. Precautions for Approach— Voltages from 301 V to 72.5 kV 

At voltages from 301 V to 72.5 kV, employees shall be protected from phase-to-phase and phase- 
to-ground differences in electric potential. 

a. When exposed grounded lines, conductors, or parts are in the work area, they shall be guarded 
or insulated. 

b. When the Rubber Glove Work Method is employed, rubber insulating gloves, insulated for the 
| maximum use voltage as listed in Table 441-6, shall be worn whenever employees are in the 

vicinity of energized conductors or parts, supplemented by one of the following two protective 
methods: 

(1) The employee shall wear rubber insulating sleeves, insulated for the maximum use voltage 
as listed in Table 441-6, in addition to the rubber insulating gloves. 

EXCEPTION: When work is performed on electric supply equipment energized at 750 V or less, 
rubber sleeves are not required if only the live parts being worked on are exposed. 

(2) All exposed energized lines or parts, other than those temporarily exposed to perform 
work and maintained under positive control, located within maximum reach of the em- 
ployee's work position, shall be covered with insulating protective equipment. 
EXCEPTION: When work is being performed on parts energized between 300 V and 750 V within 
enclosed spaces, (e.g., control panels and relay cabinets), insulating or guarding of all exposed 
grounded lines, conductors, or parts in the work area is not required provided that employees use 
insulated tools and/or gloves and that exposed grounded lines, conductors, or parts are covered to 
the extent feasible. 

c. When the Rubber Glove Work Method is employed at voltages above 15 kV phase-to-phase, 
supplementary insulation (e.g., insulated aerial device or structure-mounted insulating work 
platform), tested for the voltage involved shall be used to support the worker. 

d. Cover-up rated for the voltage involved, when used, shall be applied to the exposed facilities 

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441A3d PART 4. RULES FOR THE OPERATION OF ELECTRIC LINES 441A6a2 



as the employee first approaches the facilities from any direction, be that from the structure or 
from an aerial device, and shall be removed in the reverse order. This protective cover-up shall 
extend beyond the reach of the employee's anticipated work position or extended reach 
distance. 

4. Transient Overvoltage Control Above 72.5 kV 

a. For 121 kV to 362 kV single break per pole switching devices with three phase reclosing into 
trapped charges the maximum per-unit values given in the table (3 per unit for 121 to 362 kV) 
may increase significantly. Minimum approach distances for these devices shall be determined 
by a transient overvoltage study. 

NOTE: These overvoltages will not exceed the values of Table 441-1 if reclosing is blocked. 

b. For voltages above 72.5 kV, the minimum approach distance may be reduced if the maximum 
anticipated transient overvoltage is known for the work site. Engineering analysis is required 
when transient overvoltage control techniques are employed. When preinsertion resistors are 

| employed, they shall be operational. The minimum approach distances derived from Tables 

441-2, 441-3, and 441-4 may be used. When a reduced clearance distance from Tables 441-2, 
441-3, and 441-4 is used for a specific per-unit transient overvoltage, the maximum transient 
overvoltage shall be controlled at the work site by one of the following methods: 

| 1 . The operation of a circuit breaker or other switching device shall be modified, including 

blocking reclosing. 

| 2. The overvoltage itself shall be forcibly held to an acceptable level by the installation of 

temporary transient voltage protective devices such as surge arresters or temporary pro- 
tective gaps. 

j 3. The operation of the system shall be changed to restrict potential overvoltages resulting 

from the effect of activity on the system (e .g . , capacitor switching , tap changing , cable de- 
energization, etc.). 

5. Altitude Correction 

The distances in Tables 441-1, 441-2, 441-3, and 441-4 shall be used at elevations below 900 m 
(3000 ft). Above that altitude, the minimum approach distance shall be increased by: 

a. Multiplying the electrical component of the minimum approach' distance by the applicable al- 
titude correction factors of Table 441-5, and 

b. Adding the result to the values for inadvertent movement required by Rule 441A6a(3). 

NOTE: The electrical component of clearance included in Tables 441-1, 441-2, 441-3, and 441-4 is the 
table value less the value for inadvertent movement for that voltage shown in Rule 441A6a(3). 

6. Calculation of Approach Distances 

a. Minimum approach distances shown in Tables 441-2, 441-3, and 441-4 are calculated in feet 
to two decimal places. The second decimal place is rounded up if the third decimal place is 
other than zero. The metric values shown in these tables are derived directly from rod gap data 
originally recorded in metric measurements. For this reason, the english-unit tables do not ex- 
actly convert into the values shown in the metric tables. Because the original rod gap data for 
voltages from 1 .1 to 72 kV is measured in metric units, the values in Table 441-1 are derived 
from metric and converted to feet and inches. The following processes are used: 

1 . When converting to feet and inches, the decimal part of a foot is converted to inches and 
rounded up if the first decimal place is other than zero. 

2. When converting from feet to metric, the feet dimension from Rule 441A5a above is con- 
verted to meters. The second decimal place shall be rounded up if the third decimal place 
is other than zero. 

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441A6a3 



PART 4. RULES FOR THE OPERATION OF ELECTRIC LINES 



T-441-1 



3. Minimum approach distances calculated under this rule for 0.301 kV to 0.750 kV contain 
the electric component plus 0.31 m (1 ft) for inadvertent movement. Voltages 0.751 kV 
to 72.5 kV contain the electric component plus 0.61 m (2 ft) for inadvertent movement. 
Above 72.5 kV, the inadvertent movement distance is 0.31 m (1 ft). 

4 . Table 4 (Alternating Current) and Table 5 (Direct Current) of IEEE Std 5 1 6- 1 987 are the 
electrical basis for approach distances for voltages above 72.5 kV. IEEE Std 516-1987 
includes the formula used to derive electrical clearance distances. IEEE Std 4-1995 is the 
basis for the approach distances for voltages below 72.5 kV. 

5. The voltage ranges are contained in ANSI C84. 1-1995, Table 1 . 

Interpolation between the values contained in Tables 441-2 through 441-4 is not permitted. 
Minimum approach distances for maximum phase-to-phase voltages other than those con- 
tained in Tables 441-2 through 441-4 shall be determined using the process outlined in Rule 
441A5a. The approach distances of Table 441-1 shall be used unless the per-unit transient ov- 
ervoltage is known and controlled. 



Table 441-1 
AC Live Work Minimum Approach Distance 

(See Rule 441 in its entirety.) 



Voltage in kilovolts 
phase to phase 1,2 


Distance to employee 


Phase to ground 


Phase to phase 


(m) : (fl-in) 


lm> If't-bi) 


to 0.050 1 


not specified 


not specified 


0.051 to 0.300 1 


avoid contact 


avoid contact 


0.301 to 0.750 1 


0.31 


2-2 


0.31 


■/■■ ■ 1-0 .-.' :.:■'■; 
2-3 
2-10 


0.751 to 15 


0.65 


0.67 


15.1 to 36.0 


0.77 


2-7 


0.86 


36.1 to 46.0 


0.84 


2-9 

3-3 3 : 

3-2-* 


0.96 


3-2 

:..■ .4^.3, :,-. 

4 ii 

5-8 


46.1 to 72.5 


1.00 3 


1.20 


72.6 to 121 


0.95 3 


1.29 


138 to 145 


1.09 


3-7 


1.50 


161 to 169 


1.22 


4 11 


1.71 


230 to 242 


1.59 


5-3 


2.27 


7 ,', 


345 to 362 


2.59 


8-6 

1 1 - .< 


3.80 


12-6 

-■.;■-.■■. I8-1 -.'.■'.■ v 


500 to 550 


3.42 


5.50 


765 to 800 


4.53 


14-11 


7.91 


:mi 



1 For single-phase systems, use the highest voltage available. 

2 For single-phase lines off three phase systems, use the phase-to-phase voltage of the system. 

3 The 46.1 to 72.5 kV phase-to-ground 3-3 distance contains a 1-3 electrical component and a 2-0 
inadvertent movement component while the 72.6 to 121 kV phase-to-ground 3-2 distance contains a 
2-2 electrical component and a 1-0 inadvertent movement component. 



228 
Copyright © 2001 IEEE. All rights reserved. 



T-441-2(m) 



PART 4. RULES FOR THE OPERATION OF ELECTRIC LINES 



T-441-2(m) 



m 



Table 441-2 
AC Live Work Minimum Approach Distance With Transient Overvoltage Factor 

(See Rule 441 in its entirety.) 



Maximum 

anticipated per-unit 

transient 

overvoltage 


Distance to employee in meters, phase-to-ground 


Air, bare-hand, and clear live-line tool 


Maximum phase-to-phase voltage in kilovolts 




121 


145 


169 


242 


362 


550 


800 


1.5 












1.82 


2.95 


1.6 












1.97 


3.23 


1.7 












2.13 


3.54 


1.8 












2.29 


3.86 


1.9 












2.47 


4.19 


2.0 


0.74 


0.83 


0.92 


1.16 


1.59 


2.65 


4.53 


2.1 


0.76 


0.85 


0.95 


1.21 


1.65 


2.83 




2.2 


0.78 


0.88 


0.98 


1.25 


1.74 


3.01 




2.3 


0.80 


0.91 


1.01 


1.29 


1.84 


3.20 




2.4 


0.82 


0.93 


1.04 


1.33 


1.94 


3.42 




2.5 


0.84 


0.96 


1.07 


1.38 


2.04 






2.6 


0.86 


0.98 


1.10 


1.42 


2.14 






2.7 


0.88 


1.01 


1.13 


1.45 


2.25 






2.8 


0.91 


1.03 


1.16 


1.50 


2.36 






2.9 


0.93 


1.06 


1.19 


1.54 


2.47 






3.0 


0.95 


1.09 


1.22 


1.59 


2.59 







229 
Copyright © 2001 IEEE. All rights reserved. 



T-441-2(ft) 



PART 4. RULES FOR THE OPERATION OF ELECTRIC LINES 



T-441-2(ft) 



Table 441-2 
AC Live Work Minimum Approach Distance With Transient Overvoltage Factor 

(See Rule 441 in its entirety.) 



ft 



Maximum 
anticipated per-unit 
transient overvoltage 


Distance to employee in feet-inches, phase-to-ground 


Air, bare-hand, and clear live-line tool 


Maximum phase-to-phase voltage in kilovolts 




121 


145 


169 


242 


362 


550 


800 


1.5 












6-0 


9-8 


1.6 












6-6 


10-8 


1.7 












7-0 


11-8 


1.8 












7-7 


12-8 


1.9 












8-1 


13-9 


2.0 


2-5 


2-9 


3-0 


3-10 


5-3 


8-9 


14-11 


2.1 


2-6 


2-10 


3-2 


4-0 


5-5 


9-4 




2.2 


2-7 


2-11 


3-3 


4-1 


5-9 


9-11 




2.3 


2-8 


3-0 


3-4 


4-3 


6-1 


10-6 




2.4 


2-9 


3-1 


3-5 


4-5 


6-4 


11-3 




2.5 


2-9 


3-2 


3-6 


4-6 


6-8 






2.6 


2-10 


3-3 


3-8 


4-8 


7-1 






2.7 


2-11 


3^ 


3-9 


4-10 


7-5 






2.8 


3-0 


3-5 


3-10 


4-11 


7-9 






2.9 


3-1 


3-6 


3-11 


5-1 


8-2 






3.0 


3-2 


3-7 


4-0 


5-3 


8-6 







230 
Copyright © 2001 IEEE. All rights reserved. 



T-441-3(m) 



PART 4. RULES FOR THE OPERATION OF ELECTRIC LINES 



T-441-3(m) 



m 



Table 441-3 
AC Live Work Minimum Approach Distance With Transient Overvoltage Factor 

(See Rule 441 in its entirety.) 



Maximum 
anticipated per-unit 
transient overvoltage 


Distance to employee in meters, phase-to-phase 


Air, bare-hand, and clear live-line tool 


Maximum phase-to-phase voltage in kilovolts 




121 


145 


169 


242 


362 


550 


800 


1.5 












2.24 


3.67 


1.6 












2.65 


4.42 


1.7 












3.08 


5.23 


1.8 












3.53 


6.07 


1.9 












4.01 


6.97 


2.0 


1.08 


1.24 


1.41 


1.85 


2.61 


4.52 


7.91 


2.1 


1.10 


1.27 


1.44 


1.89 


2.68 


4.75 




2.2 


1.12 


1.29 


1.47 


1.93 


2.78 


4.98 




2.3 


1.14 


1.32 


1.50 


1.97 


2.90 


5.21 




2.4 


1.16 


1.35 


1.53 


2.01 


3.02 


5.50 




2.5 


1.18 


1.37 


1.56 


2.06 


3.14 






2.6 


1.21 


1.40 


1.59 


2.10 


3.27 






2.7 


1.23 


1.43 


1.62 


2.13 


3.40 






2.8 


1.25 


1.45 


1.65 


2.19 


3.53 






2.9 


1.27 


1.48 


1.68 


2.22 


3.67 






3.0 


1.29 


1.50 


1.71 


2.27 


3.80 







I 



231 
Copyright © 2001 IEEE. All rights reserved. 



T-441-3(ft) 



PART 4. RULES FOR THE OPERATION OF ELECTRIC LINES 



T-441-3(ft) 



ft 



Table 441-3 
AC Live Work Minimum Approach Distance With Transient Overvoltage Factor 

(See Rule 441 in its entirety.) 



Maximum 
anticipated per-unit 
transient overvoltage 


Distance to employee in feet-inches, phase-to-phase 


Air, bare-hand, and clear live-line tool 


Maximum phase-to-phase voltage in kilovolts 




121 


145 


169 


242 


362 


550 


800 


1.5 












1^ 


12-1 


1.6 












8-9 


14-6 


1.7 












10-2 


17-2 


1.8 












11-7 


19-11 


1.9 












13-2 


22-11 


2.0 


3-7 


4-1 1 


4-8 


6-1 


8-7 


14-10 


26-0 


2.1 


3-7 


4-2 


4-9 


6-3 


8-10 


15-7 




2.2 


3-8 


4-3 


4-10 


6-A 


9-2 


16-4 




2.3 


3-9 


4-4 


4-11 


6-6 


9-6 


17-2 




2.4 


3-10 


4-5 


5-0 


6-7 


9-11 


18-1 




2.5 


3-11 


4-6 


5-2 


6-9 


10^1 






2.6 


4-0 


4-7 


5-3 


6-11 


10-9 






2.7 


4-1 


4-8 


5-4 


7-0 


11-2 






2.8 


4-1 


4-9 


5-5 


7-2 


11-7 






2.9 


4-2 


4-10 


5-6 


7-4 


12-1 






3.0 


4-3 


4-11 


5-8 


7-6 


12-6 







232 
Copyright © 2001 IEEE. All rights reserved. 



T-441-4(m) 



PART 4. RULES FOR THE OPERATION OF ELECTRIC LINES 



T-441-4(ft) 



m 



Table 441-4 
DC Live Work Minimum Approach Distance With Transient Overvoltage Factor 

(See Rule 441 in its entirety.) 



Maximum anticipated 

per-unit transient 

overvoltage 


Distance to employee in meters, conductor to ground 


Air, bare-hand, and clear live-line tool 


Maximum conductor-to-ground voltage in kilovolts 




250 


400 


500 


600 


750 


1 .5 or lower 


1.12 


1.60 


2.06 


2.62 


3.61 


1.6 


1.17 


1.69 


2.24 


2.86 


3.98 


1.7 


1.23 


1.82 


2.42 


3.12 


4.37 


1.8 


1.28 


1.95 


2.62 


3.39 


4.79 



Table 441-4 
DC Live Work Minimum Approach Distance With Transient Overvoltage Factor 

(See Rule 441 in its entirety.) 



ft 



Maximum anticipated 

per-unit transient 

overvoltage 


Distance to employee in meters, conductor to ground 


Air, bare-hand, and clear live-line tool 


Maximum conductor-to-ground voltage in kilovolts 




250 


400 


500 


600 


750 


1 .5 or lower 


3-8 


5-3 


6-9 


8-7 


11-10 


1.6 


3-10 


5-7 


7-4 


9-5 


13-1 


1.7 


4-1 


6-0 


7-11 


10-3 


14-4 


1.8 


4-3 


6-5 


8-7 


11-2 


15-9 



I 



233 
Copyright © 2001 IEEE. All rights reserved. 



T-441-5 



PART 4. RULES FOR THE OPERATION OF ELECTRIC LINES 



T-441-6 



Table 441-5 
Altitude Correction Factor 

(See Rule 441 in its entirety.) 



Altitude 


Correction factor 


(m) 


m» 


900 i 3000 


LOO 


1200 


4000 


1.02 


1 500 .'■..'.'■.■.■:■ 5000 ■ : : L ■ : ■ 


1.05 


1800 


6000 


1.08 


2100 


7000 i 

mm 

9000 

ioooo : 

12 000 

■:■ . : .; .14000' :>;■.' ;[; : .'. ; 

16 000 

r 18 000 

20 000 


1.11 


2400 


1.14 


2700 


1.17 


3000 


1.20 


3600 


1.25 


4200 


1.30 


4800 


1.35 


5400 


1.39 


6000 


1.44 



Table 441-6 
Maximum Use Voltage for Rubber Insulating Equipment 



Class of Equipment 


Maximum Use Voltage 1 


00 


500 





1000 


1 


7500 


2 


17 000 


3 


26 500 


4 


36 000 



The maximum use voltage is the ac voltage (rms) rating of the protective equipment that designates the 
maximum nominal design voltage of the energized system that may be safely worked. The nominal design 
voltage is equal to the phase-to-phase voltage on multiphase circuits. 

EXCEPTION 1: If there is no multiphase exposure in a system area (at the worksite) and the voltage 
exposure is limited to the phase (polarity on dc systems) to ground potential, the phase (polarity on dc 
systems) to ground potential shall be considered to be the nominal design voltage. 

EXCEPTION 2: If electric equipment and devices are insulated, isolated, or both, such that the 
multiphase exposure on a grounded wye circuit is removed and if supplemental insulation (e.g., insulated 
aerial device or structure-mounted insulating work platform) is used to insulate the employee from 
ground, then the nominal design voltage may be considered as the phase-to-ground voltage on that 
circuit. 



234 
Copyright © 2001 IEEE. All rights reserved. 



441B PART 4. RULES FOR THE OPERATION OF ELECTRIC LINES 441C2 



B. Additional Approach Requirements 

1 . The clear insulation distance associated with insulators shall be the shortest straight-line air-gap 
distance from the nearest energized part to the nearest grounded part. 

2. When working on insulators under live work procedures employing rubber gloves or live-line 
tools (hot sticks), the clear insulation distance shall be not less than the straight-line distance in air 
required by Tables 441-1, 441-2, 441-3, and 441-4. 

3. Work may be performed at the grounded end of an open switch if all of the following conditions 
are met: 

a. The air-gap distance of the switch shall not be reduced in any manner. This distance shall be 
not less than the electrical basis for approach distances determined by Rule 441 A6a(4) for the 
maximum anticipated transient overvoltage. The inadvertent movement values of 
Rule 441A6a(3) are not required in this distance. 

b. The minimum approach distance to the energized part of the switch shall be not less than that 
required by Rule 441 A. 

4. Special Rules for Working on Insulator Assemblies Operating Above 72.5 kV 

a. When work is to be performed at the ground end of an insulator assembly, the minimum ap- 
proach distance to the nearest energized part may equal the straight-line distance measured 
along the insulators. 

b. For suspension insulator assembly installations (see ANSI C29.2-1992) operating above 
72.5 kV, the first insulator at the grounded end may be temporarily shorted out as part of the 
work procedure. 

EXCEPTION: For voltages at 230 kV and above, up to three insulator units may be temporarily shorted 
out as part of the work procedure, provided that the minimum approach distance requirements of Rule 
441 are met. 

c. When performing live work employing the bare-hand technique on installations operating 
above 72.5 kV, the first insulator at the energized (hot) end of a suspension insulator assembly 
(see ANSI C29.2-1992) may be shorted out during the work. 

EXCEPTION: For voltages at 230 kV and above, up to three insulator units may be temporarily shorted 
out as part of the work procedure, provided that the minimum approach distance requirements of Rule 
441 are met. 

(1) The minimum approach distance to the grounded end of the insulator assembly may be 
equal to the straight-line distance from the nearest energized part to the closest grounded 
part across the insulators. 

(2) The straight-line insulation distance shall be not less than the values required by Tables 
441-1, 441-2, 441-3, and 441-4. 

C. Live-Line Tool Clear Insulation Length 

1 . Clear Live-Line Tool Length. 

The clear live-line tool distance shall be not less than the distance measured longitudinally along 
the live-line tool from the conductive part at the working end of the tool and any part of the em- 
ployee. Distances for conducting sections (such as metallic splices and hardware) shall be sub- 
tracted from the clear live-line length. The clear live-line tool length shall equal or exceed the 
values for the minimum approach distance in Tables 441-1 , 441-2, 441-3, and 441-4 for the indi- 
cated voltage ranges. The minimum clear live-line tool distance shall be the distance measured 
longitudinally along the live-line tool from the conductive part at the working end of the tool to 
any part of the employee. 

2. Live-Line Conductor Support Tool Length 

Conductor support tools such as link sticks, strain carriers, and insulator cradles may be used pro- 
vided that the clear insulating distance is at least as long as the insulator string or the maximum 
distance specified in Rule 441 A. When installing this equipment, the employee shall maintain the 
minimum approach distance required equal to the clear insulating length for the support tools. 
NOTE: Conductive components of tools disturb the field in the gap and decrease the insulation value of the 
tool more than the linear subtraction of the length(s) of the conductive components. 

235 
Copyright © 2001 IEEE. All rights reserved. 



I 



442 



PART 4. RULES FOR THE OPERATION OF ELECTRIC LINES 



442E2 



442. Switching Control Procedures 

A. Designated Person 

A designated person shall: 

1 . Keep informed of operating conditions affecting the safe and reliable operation of the system. 

2. Maintain a suitable record showing operating changes in such conditions. 

3. Issue or deny authorization for switching, as required, for safe and reliable operation. 

B. Specific Work 

Authorization from the designated person shall be secured before work is begun on or in the vicinity 
of station equipment, transmission, or interconnected feeder circuits and where circuits are to be de- 
energized at stations. The designated person shall be notified when such work ceases. 
EXCEPTION 1 : In an emergency , to protect life or property , or when communication with the designated person 
is difficult because of storms or other causes, any qualified employee may make repairs on or in the vicinity of 
the equipment or lines covered by this rule without special authorization if the qualified employee can clear the 
trouble promptly with available help in compliance with the remaining rules. The designated person shall there- 
after be notified as soon as possible of the action taken. 

EXCEPTION 2: Suspension of normal rule or rules under disaster conditions: Where catastrophic service disrup- 
tions occur (e.g., earthquake, hurricane) and where multiple employer crews may be imported to assist in service 
restorations, the normal use of Rule 442 procedures may be suspended provided that: 

1 . Each individual involved in system repairs is informed of the suspension of normal rules. 

2. Employees are required to observe all requirements of Rule 443 and Rule 444, including protection desig- 
nated from step and touch potentials. 

3 . Equipment used to de-energize or re-energize circuits at designated points of control (e .g . , station breakers) , 
is operated in conformance with Rule 442A, and Rule 442D. 

4. Tagging requirements under Rule 444C, for this EXCEPTION, shall include, and may be limited to, desig- 
nated points of control. 

C. Operations at Stations 

Qualified employees shall obtain authorization from the designated person before switching sections 
of circuits. 

In the absence of specific operating schedules, employees shall secure authorization from the des- 
ignated person before opening and closing supply circuits or portions thereof or starting and stopping 
equipment affecting system operation at stations. 

EXCEPTION 1 : Sections of distribution circuits are excepted if the designated person is notified as soon as pos- 
sible after the action is taken. 

EXCEPTION 2: In an emergency, to protect life or property, any qualified employee may open circuits and stop 
moving equipment without special authorization if, in the judgment of the qualified employee, this action will 
promote safety, but the designated person shall be notified as soon as possible of such action, with reasons 
therefore. 

D. Re-energizing After Work 

Instructions to re-energize equipment or lines that have been de-energized by permission of the des- 
ignated person shall not be issued by the designated person until all employees who requested the line 
to be de-energized have reported clear. Employees who have requested equipment or lines de-ener- 
gized for other employees or crews shall not request that equipment or lines be re-energized until all 
of the other employees or crews have reported clear. The same procedure shall be followed when more 
than one location is involved. 



E. Tagging Electric Supply Circuits Associated With Work Activities 

1 . Equipment or circuits that are to be treated as de-energized and grounded per Rule 444D shall 
have suitable tags attached to all points where such equipment or circuits can be energized. 

2. When the automatic reclosing feature of a reclosing device is disabled during the course of work 

236 
Copyright © 2001 IEEE. All rights reserved. 



441E2 PART 4. RULES FOR THE OPERATION OF ELECTRIC LINES 443A4b 



on energized equipment or circuits, a tag shall be placed at the reclosing device location. 
EXCEPTION: If the automatic reclosing feature of a reclosing device is disabled by a Supervisory Control 
and Data Acquisition System (SCADA), the system shall provide for the following: 

a. At the SCADA Operating Point 

(1) A signal is received by the SCADA operator confirming that the disabling operation has occurred 
at the reclosing device location, and 

(2) A readily visible tag or electronic display is used to inform any potential SCADA operator that a 
disabling operation has been initiated, and 

(3) The tag or electronic display is removed before action is taken to reenable the automatic reclosing 
feature. 

b. At the Reclosing Device Location 

(1) The reclosing feature is disabled in such a manner as to prevent manual override of the normal con- 
trol by any potential on-site operator, or 

(2) A signal, flag, or other display is used in such a manner as to alert any potential on-site operator that 
the reclosing feature has been disabled. 

3. The required tags shall be placed to clearly identify the equipment or circuits on which work is 
being performed. 

F. Restoration of Service After Automatic Trip 

1 . When circuits or equipment upon which tags have been placed open automatically, the circuits or 
equipment shall be left open until reclosing has been authorized. 

2. When circuits open automatically, local operating rules shall determine in what manner and how 
many times they may be closed with safety. 

G. Repeating Oral Messages 

Each employee receiving an oral message concerning the switching of lines and equipment shall im- 
mediately repeat it back to the sender and obtain the identity of the sender. Each employee sending 
such an oral message shall require it to be repeated back by the receiver and secure the latter' s identity. 

443. Work on Energized Lines and Equipment 

A. General Requirements 

1. When working on energized lines and equipment, one of the following safeguards shall be 
applied: 

a. Insulate employee from energized parts 

b. Isolate or insulate the employee from ground and grounded structures, and potentials other 
than the one being worked on. 

2. Employees shall not place dependence for their safety on the covering (nonrated insulation) of 
wires. All precautions (see Section 44) for working on energized parts shall be observed. 

3 . All employees working on or in the vicinity of lines or equipment exposed to voltages higher than 
those guarded against by the safety protective equipment provided shall assure themselves that the 
equipment or lines on which they are working are free from dangerous leakage or induction, or 
have been effectively grounded. 

4. Cutting Into Insulating Coverings of Energized Conductors 

a. A supply cable to be worked on as de-energized that cannot be positively identified or deter- 
mined to be de-energized shall be pierced or severed at the work location with a tool designed 
for the purpose. 

b. Before cutting into an energized supply cable, the operating voltage shall be determined and 
appropriate precautions taken for handling conductors at that voltage. 

237 
Copyright © 2001 IEEE. All rights reserved. 



I 



443A4c PART 4. RULES FOR THE OPERATION OF ELECTRIC LINES 443H 



c . When the insulating covering on energized wires or cables must be cut into , the employee shall 
use a tool designed for the purpose. While doing such work, suitable eye protection and insu- 
lating gloves with protectors shall be worn. Employees shall exercise extreme care to prevent 
short-circuiting conductors when cutting into the insulation. 

5. Metal measuring tapes, and tapes or ropes containing metal threads or strands, shall not be used 
closer to exposed energized parts than the distance specified in Rule 441 A. Care should be taken 
when extending metallic ropes or tapes parallel to and in the proximity of high-voltage lines be- 
cause of the effect of induced voltages. 

6. Equipment or material of a noninsulating substance that is not bonded to an effective ground and 
which extends into an energized area, and which could approach energized equipment closer than 
the distance specified in Rule 441 A, shall be treated as though it is energized at the same voltage 
as the line or equipment to which it is exposed. 

B. Requirement for Assisting Employee 

In inclement weather or at night, no employee shall work alone outdoors on or dangerously in the vi- 
cinity of energized conductors or parts of more than 750 V between conductors. 
EXCEPTION: This shall not preclude a qualified employee, working alone, from cutting trouble in the clear, 
switching, replacing fuses, or similar work if such work can be performed safely. 

C. Opening and Closing Switches 

Manual switches and disconnectors shall always be closed by a continuous motion. Care should be 
exercised in opening switches to avoid serious arcing. 

D. Working Position 

Employees should avoid working on equipment or lines in any position from which a shock or slip 
will tend to bring the body toward exposed parts at a potential different than the employee's body. 
Work should, therefore, generally be done from below, rather than from above. 

E. Protecting Employees by Switches and Disconnectors 

When equipment or lines are to be disconnected from any source of electric energy for the protection 
of employees, the switches, circuit breakers, or other devices designated and designed for operation 
under the load involved at sectionalizing points shall be opened or disconnected first. When re-ener- 
gizing, the procedure shall be reversed. 

F. Making Connections 

In connecting de-energized equipment or lines to an energized circuit by means of a conducting wire 
or device, employees should first attach the wire to the de-energized part. When disconnecting, the 
source end should be removed first. Loose conductors should be kept away from exposed energized 
parts. 

G. Switchgear 

Switchgear shall be de-energized and grounded per Rule 444D prior to performing work involving 
removal of protective barriers unless other suitable means are provided for employee protection. The 
personnel safety features in switchgear shall be replaced after work is completed. 

H. Current Transformer Secondaries 

The secondary of a current transformer shall not be opened while energized . If the entire circuit cannot 
be properly de-energized before working on an instrument, a relay, or other section of a current 
transformer secondary circuit, the employee shall bridge the circuit with jumpers so that the current 
transformer secondary will not be opened. 

238 
Copyright © 2001 IEEE. All rights reserved. 



4431 PART 4. RULES FOR THE OPERATION OF ELECTRIC LINES 444C 



I. Capacitors 

Before employees work on capacitors, the capacitors shall be disconnected from the energizing 
source, short-circuited, and grounded. Any line to which capacitors are connected shall be short-cir- 
cuited and grounded before it is considered de-energized. Since capacitor units may be connected in 
series-parallel, each unit shall be shorted between all insulated terminals and the capacitor tank before 
handling. Where the tanks of capacitors are on ungrounded racks, the racks shall also be grounded. 
The internal resistor shall not be depended upon to discharge capacitors. 

J. Gas-Insulated Equipment 

Employees working on gas-insulated cable systems or circuit breakers shall be instructed concerning 
the special precautions required for possible presence of arcing by-products of sulfur-hexafluoride 

(SF 6 ). 

NOTE: By-products resulting from arcing in sulfur-hexafluoride (SF 6 ) gas-insulated systems are generally toxic 
and irritant. Gaseous by-products can be removed for maintenance on the compartments by purging with air or 
dry nitrogen. The solid residue that must be removed is mostly metallic fluoride. This fine powder absorbs mois- 
ture and produces fluorides of sulfur and hydrofluoric acid, which are toxic and corrosive. 

K. Attendant on Surface 

While electric supply personnel are in a manhole, an employee shall be available on the surface in 
the immediate vicinity to render assistance from the surface. This shall not preclude the employee on 
the surface from entering the manhole to provide short-term assistance. 

EXCEPTION: This shall not preclude a qualified employee, working alone, from entering a manhole where en- 
ergized cables or equipment are in service, for the purpose of inspection, housekeeping, taking readings, or sim- 
ilar work if such work can be performed safely. 

L. Unintentional Grounds on Delta Circuits 

Unintentional grounds on delta circuits shall be removed as soon as practical. 

444. De-energizing Equipment or Lines to Protect Employees 

A. Application of Rule 

1 . When employees must depend on others to operate switches or otherwise de-energize circuits on 
which they are to work, or must secure special authorization before they operate such switches 
themselves, the precautionary measures that follow shall be taken in the order given before work 
is begun. 

2. If the employee under whose direction a section of a circuit is disconnected is in sole charge of 
the section and of the means of disconnection, those portions of the following measures that per- 
tain to dealing with the designated person may be omitted. 

3. Records shall be kept on all contractual utility interactive systems on any electric supply lines. 
When these lines are de-energized according to Rule 444C, the utility interactive system shall be 
visibly disconnected from the lines. 

B . Employee ' s Request 

The employee in charge of the work shall apply to the designated person to have the particular section 
of equipment or lines de-energized, identifying it by position, letter, color, number, or other means. 

C. Operating Switches, Disconnectors, and Tagging 

The designated person shall direct the operation of all switches and disconnectors through which 
electric energy may be supplied to the particular section of equipment and lines to be de-energized, 
and shall direct that such switches and disconnectors be rendered inoperable and tagged. If switches 
that are controlled automatically or remotely or both can be rendered inoperable, they shall be tagged 
at the switch location. If it is impractical to render such switches and disconnectors inoperable, then 
these remotely controlled switches shall also be tagged at all points of control. A record shall be made 
when placing the tag, giving the time of disconnection, the name of the person making the discon- 

239 
Copyright © 2001 IEEE. All rights reserved. 



I 



A 



444D PART 4. RULES FOR THE OPERATION OF ELECTRIC LINES 444H 



nection, the name of the employee who requested the disconnection, and the name or title or both, of 
the designated person. 

D. Employee's Protective Grounds 

When all the switches and disconnectors designated have been operated, rendered inoperable where 
practical, and tagged in accordance with Rule 444C, and the employee has been given permission to 
work by the designated person, the employee in charge should immediately proceed to make the em- 
ployee's own protective grounds or verify that adequate grounds have been applied (see Rule 445) 
on the disconnected lines or equipment. During the testing for potential and/or application of grounds , 
distances not less than those shown in Tables 441-1 to 441-3, as applicable, shall be maintained. 

Grounds shall be placed at each side of the work location and as close as practical to the work 
location, or a single point ground shall be placed at the work location. If work is to be performed at 
more than one location on a line section, the line section shall be grounded and short-circuited at one 
location in the line section and the conductor to be worked on shall be grounded at each work 
location. 

The distance in Tables 441-1 , 441-2, or 441-3, as applicable, shall be maintained from unground- 
ed conductors at the work location. Where the making of a ground is impractical, or the conditions 
resulting therefrom are more hazardous than working on the lines or equipment without grounding, 
the ground may be omitted by special permission of the designated person. 

E. Proceeding With Work 

1 . After the equipment or lines have been de-energized and grounded per Rule 444D, the employee 
in charge, and those under the direction of the employee in charge, may proceed with work on the 
de-energized parts. 

Equipment may be re-energized for testing purposes only under the supervision of the employee 
in charge and subject to authorization by the designated person. 

2. Each additional employee in charge desiring the same equipment or lines to be de-energized and 
grounded per Rule 444D for the protection of that person, or the persons under direction, shall 
follow these procedures to secure similar protection. 

F. Reporting Clear— Transferring Responsibility 

1 . The employee in charge , upon completion of the work and after ensuring that all persons assigned 
to this employee in charge are in the clear, shall remove protective grounds and shall report to the 
designated person that all tags protecting that person may be removed. 

2. The employee in charge who received the permission to work may, if specifically permitted by 
the designated person, transfer the permission to work and the responsibility for persons by per- 
sonally informing the affected persons of the transfer. 

G. Removal of Tags 

1 . The designated person shall then direct the removal of tags and the removal shall be reported back 
to the designated person by the persons removing them. Upon the removal of any tag, there shall 
be added to the record containing the name of the designated person or title or both, and the person 
who requested the tag, the name of the person requesting removal, the time of removal, and the 
name of the person removing the tag. 

2. The name of the person requesting removal shall be the same as the name of the person requesting 
placement, unless responsibility has been transferred according to Rule 444F. 

H. Sequence of Re-energizing 

Only after all protective grounds have been removed from the circuit or equipment and after protec- 
tive tags have been removed in accordance with Rule 444G at a specific location, may the designated 
person direct the operation of switches and disconnectors at that location. 

240 
Copyright © 2001 IEEE. All rights reserved. 



445 PART 4. RULES FOR THE OPERATION OF ELECTRIC LINES 446A 

445. Protective Grounds 

A. Installing Grounds 

When placing protective grounds on a previously energized part, the following sequence and precau- 
tionary measures shall be observed. 

EXCEPTION: In certain situations, such as when grounding conductors are supported on some high- voltage 
towers, it may be appropriate to perform the voltage test before bringing the grounding device into the work area. 

1 . Current-Carrying Capacity of Grounds 

The grounding device shall be of such size as to carry the induced current and anticipated fault 
current that could flow at the point of grounding for the time necessary to clear the line. 

2. Initial Connections 

Before grounding any previously energized part, the employee shall first securely connect one 
end of the grounding device to an effective ground. Grounding switches may be employed to con- 
nect the equipment or lines being grounded to the actual ground connections. 

3. Test for Voltage 

The previously energized parts that are to be grounded shall be tested for voltage except where 
previously installed grounds are clearly in evidence. The employee shall keep every part of the 
body at the required distance by using insulating handles of proper length or other suitable 
devices. 

4. Completing Grounds 

a. If the part shows no voltage, the grounding may be completed. 

b. If voltage is present, the source shall be determined to ensure that presence of this voltage 
does not prohibit completion of the grounding. 

c. After the initial connections are made to ground, the grounding device shall next be brought 
into contact with the previously energized part using insulating handles or other suitable de- 
vices and securely clamped or otherwise secured thereto. Where bundled conductor lines are 
being grounded, grounding of each subconductor should be made. Only then may the employ- 
ee come within the distances from the previously energized parts specified in Rule 441 A or 
proceed to work upon the parts as upon a grounded part. 

B. Removing Grounds 

The employee shall first remove the grounding devices from the de-energized parts using insulating 
handles or other suitable devices. 

Extreme caution shall be exercised that the proper sequence of installing or removing grounds is 
followed. The connection to the effective ground shall not be removed first. If done, electric shock 
and injury may result. 

446. Live Work 

All employees using live work practices shall observe the following rules in addition to applicable 
rules contained elsewhere in Sections 42 and 44. 

The distances specified in Tables 441-1, 441-2, 441-3, or 441-4 shall be maintained from all 
grounded objects and from other conductors, lines, and equipment having a potential different from 
that to which conductive equipment and devices are bonded in order to maintain the equipotentially 
energized work environment in an isolated state. 

A. Training 

Employees shall be trained in live work practices, which include rubber glove, hot stick, or bare-hand 
method, before being permitted to use these techniques on energized lines. 

241 
Copyright © 2001 IEEE. All rights reserved. 






446B PART 4. RULES FOR THE OPERATION OF ELECTRIC LINES 447 



B. Equipment 

1 . Insulated aerial devices, ladders, and other support equipment used in live work shall be evaluated 
for performance at the voltages involved. Tests shall be conducted to ensure the equipment's in- 
tegrity. Insulated aerial devices used in bare-hand work shall be tested before the work is started 
to ensure the integrity of the insulation. See applicable references in Section 3, specifically 
IEEE Std 516-1987 and ANSI/SIA A92.2-1992. 

2. Insulated aerial devices and other equipment used in this work shall be maintained in a clean 
condition. 

3 . Tools and equipment shall not be used in a manner that will reduce the overall insulating strength 
of the insulated aerial device. 

C. When working on insulators under live-line procedures, the clear insulation distance shall be not less 
than the distances required by Tables 441-1 , 441-2, 441-3, and 441-4. 

D. Bonding and Shielding for Bare-Hand Method 

1 . A conductive bucket liner or other suitable conducting device shall be provided for bonding the 
insulated aerial device to the energized line or equipment. 

2. The employee shall be bonded to the insulated aerial device by use of conducting shoes, leg clips, 
or other suitable means. 

3 . Adequate electrostatic shielding in the form of protective clothing that has been evaluated for elec- 
trical performance shall be provided and used where necessary. 

NOTE: Electrostatic Shielding. Evaluation of protective clothing designed for this purpose is covered in 
IEEE Std 516-1987. 

4. Before the employee contacts the energized part to be worked on, the aerial device shall be bonded 
to the energized conductor by means of a positive connection. 

447. Protection Against Arcing and Other Damage While I retaliating and Maintaining 
Insulators and Conductors 

In installing and maintaining insulators and conductors, precautions shall be taken to limit the oppor- 
tunity for, as far as is practical, any damage that might render the conductors or insulators liable to 
fall. Precautions shall also be taken to prevent, as far as is practical, any arc from forming and to pre- 
vent any arc that might be formed from injuring or burning any parts of the supporting structures, in- 
sulators, or conductors. 



242 
Copyright © 2001 IEEE. All rights reserved. 



APPENDIX A 



Appendix A 

I (This Appendix is not part of Accredited Standards Committee C2-2002, National Electrical Safety Code, 
2002 Edition, and is included for information only.) 

Uniform System of Clearances 
Adopted in the 1990 Edition 

Rules 232, 233, and 234 
Introduction 

The original format or system for stating NESC requirements was developed before 1920 and recognized 
the practical constraints of that time: Clearances were specified for a set of basic conditions. Some basic 
clearances included conductor movement; adders were used for nonbasic conditions. Although easy to use, 
it was unduly conservative in many cases and did not adequately recognize new materials and construction 
in others. Various additional clearance requirements were added over the years. 
J For the 1990 edition, an intensive study by the NESC Clearances Subcommittee identified: 

• Modern utility practices and capabilities that remove the previous clearance measurement constraints, 

• Apparent inconsistencies in certain clearance treatments, and 

• The need to develop a uniform clearance system independent of materials used for conductors and ca- 
bles, stringing tensions, operating temperatures, and similar constraints. 

| The new uniform clearance system contained in the 1990 and subsequent editions reflects the dimensions 
of expected activities in each area (reference component), as well as the relative potential problem caused by 
each type of facility (mechanical and electrical component). 

| Conductor clearance in the 1990 and subsequent editions is stated in terms of the "closest approach," i.e., 
the clear distance that must be maintained under specified conditions. 

• Vertical clearances are required during maximum sag conditions; they provide for expected activity be- 
neath a line. 

• Horizontal clearances are required when the conductor is at rest; they provide for expected activity 
alongside a line. In addition, displacement of conductors by wind is considered under certain 
conditions. 

Under the new system, users consider the actual characteristics of the materials and construction, rather 
than the reference characteristics built into the early code requirements. 

While some clearance values in the new system may appear to be larger and some smaller, the net effective 
clearances for conductors and cables are, for most of the clearance values, essentially unchanged. Some few 
values required minor adjustments of the effective clearances to make them uniform with the other values, 
thus illustrating one of the needs for these changes. 
J The 1990 and subsequent editions provide the following user benefits: 

• Simple code language in performance-standard format (as opposed to the prior design-manual style), 

• Readily understandable intent, 

• Uniform clearance values, 

• Integration of prior rules for long-span construction and/or high-conductor temperature operation, and 

• Reduced number of footnotes required to cover exceptions. 

The 1990 Changes 

Rules 232, 233, and 234 were revised based on a coordinated, uniform system of clearances developed 
under a building-block approach. Three components were considered to determine the total clearance 
required: 

• A reference component to cover activity in the area to be cleared by the overhead supply and/or com- 
munication lines. For example, truck height for over-the-road transport is limited to 4.3 m (14 ft) by 
state regulation. Thus the reference component for roads in Table 232-3 is 4.3 m (14 ft). Reference com- 
ponents included in the required clearances are shown in Table A-2. 

243 
Copyright © 2001 IEEE. All rights reserved. 



I 



APPENDIX A 



• A mechanical component appropriate for the supply or communication line item. The mechanical com- 
ponent for open supply conductors is 610 mm (2 ft) (Table A-l). 

• An electrical component appropriate for the voltage involved. The electrical component for open supply 
conductors, over 750 V to 22 kV, is 760 mm (2.5 ft) (Table A-l). 

The required clearance is the sum of the three components: thus, 5.6 m (18.5 ft) is required for open supply 
conductors, over 750 V to 22 kV, over roads (Table 232-1). For purposes of illustration, the mechanical and 
electrical components are combined in Table A-l, and items with the same total mechanical and electrical 
components are grouped into similar clearance categories. Six groups are thus created. 



244 
Copyright © 2001 IEEE. All rights reserved. 



APPENDIX A 



Table A-l 



Group 


M&E 

(mm/m) 


M&E 

(ft) 


Category 


R/NR 


GI/O 


M 


E 


I 


305 mm 


1.0 


Support Arms 


1.0/— 


0.0/— 


1.0 


0.0 






■:."Vr , ?:i. 


Effectively Grounded Equipment Cases 


1.0/— 


0.0/— 


1.0 


0.0 


n 


455 mm 


1.5 : 


Insulated Communication Conductors 
and Cables 


— /1.5 


0.0/— 


1.5 


0.0 






: vF-V ':,>'';> 


Messengers 


— /1.5 


0.0/— 


1.5 


0.0 








Surge Protection Wires 


— /1.5 


0.0/— 


1.5 


0.0 






ill;.. ";. : i* 


Grounded Guys 


— /1.5 


0.0/— 


1.5 


0.0 








230E1 


— /1.5 


0.0/— 


1.5 


0.0 








230C1 


— /1.5 


0.0/— 


1.5 


0.0 


ni 


610mm 


2.0 


URLP, V to 750 V 


1.0/— 


— /0.5 


1.5 


0.5 








Noninsulated Communication 
Conductors 


— /1.5 


— /0.5 


2.0 


0.0 








230C2, V to 750 V 


— /1.5 


0.0/— 


1.5 


0.5 








230C3, V to 750 V 


— /1.5 


0.0/— 


1.5 


0.5 






Iv'^'ii 


Ungrounded Cases of Equipment 
at to 750 V 


1.0/— 


— /0.5 


1.5 


0.5 


rv 


760 mm 


2.5 


230C2, Greater than 750 V 


— /1.5 


0.0/— 


1.5 


1.0* 








230C3, Greater than 750 V 


— /1.5 


0.0/— 


r 1.5 


1.0* 








Open Supply Conductors, to 750 V 


— /1.5 


0.0/— 


2.0 


0.5* 


V 


1.2 m 


10 


URLP, Greater than 750 V to 22 kV 


1.0/— 


—10.5 


1.5 


2.5 






W: : l Wi 


Ungrounded Cases of Equipment 
at Greater than 750 V to 22 kV 


1.0/— 


— /0.5 


1.5 


2.5 


VI 


1.37 m 


•1.5 


Open Supply Conductors, Greater than 
750 V to 22 kV 


— /1.5 


— /0.5 


2.0 


2.5 



LEGEND 

URLP 

R 

NR 

GI 

O 



Unguarded rigid live parts 

Rigid = 305 mm (1.0 ft) 

Nonrigid = 155 mm (1.5 ft) 

Grounded or insulated = 0.0 m (0.0 ft) 

Bare, ungrounded, or open conductor or part = 152 mm (0.5 ft) 
M — Mechanical component = R/NR plus GI/O 
E — Electrical Component 

• Grounded & Communication Conductor = 0.0 m (0.0 ft) 

• Supply Line V to 750 V = 152 mm (0.5 ft) 

• Supply Line Greater than 750 V to 22 kV =760 mm (2.5 ft) 
M&E — Sum of M and E values 



NOTES: (1) Ungrounded guys and ungrounded portions of guys between guy insulators have clearances 

based on the highest voltage to which they are exposed. 

(2) An asterisk (*) beside a value indicates an exception to the legend. 



I 



245 
Copyright © 2001 IEEE. All rights reserved. 



APPENDIX A 



Table A-2a 
Reference Components of Rule 232 



m 





Table 232-1 


Table 232-2 


Item 


Ref(m) 


Item 


Ref(m) 


Track rails 


1 


6.7 


— 


— 


Roads, streets, alleys, etc. 


2 


4.3 


la 


4.3 


Residential driveways, etc. 


3 


4.3 


lb 


4.3 


Other land traversed by vehicles 


4 


4.3 


lc 


4.3 


Spaces and ways — pedestrians 


5 


2.45/3.0 


Id 


3.0 


Water areas — no sailboating 


6 


3.8 


— 


— 


Water areas — sailboating 


7 




— 




(a) Less than 0.08 km 2 




4.9 




— 


(b) Over 0.08 to 0.8 km 2 




9.0 




— 


(c) Over 0.8 to 8 km 2 




9.0 




— 


(d) Over 8 km 2 




11.0 




— 


Areas posted for rigging or launching 
sailboats 


8 


See 7 


— 




Within or along: 










Roads, streets, or alleys 


9 


4.3 


2a 


4.3 


Rural districts, vehicles unlikely 


10 


3.65 


2b 


3.65 



ft 



H 



Table A-2a 
Reference Components of Rule 232 





Table 232-1 


Table 232-2 


Item 


Ref(ft) 


Item 


Ref(ft) 


Track rails 


1 


22.0 


— 


— 


Roads, streets, alleys, etc. 


2 


14.0 


la 


14.0 


Residential driveways, etc. 


3 


14.0 


lb 


14.0 


Other land traversed by vehicles 


4 


14.0 


lc 


14.0 


Spaces and ways — pedestrians 


5 


8.0/10.0 


Id 


10.0 


Water areas — no sailboating 


6 


12.5 


— 


— 


Water areas — sailboating 


7 




— 




(a) Less than 20 acres 




16.0 




— 


(b) Over 20 to 200 acres 




30.0 




— 


(c) Over 200 to 2000 acres 




30.0 




— 


(d) Over 2000 acres 




36.0 




— 


Areas posted for rigging or launching 
sailboats 


8 


See 7 


— 




Within or along: 










Roads, streets, or alleys 


9 


14.0 


2a 


14.0 


Rural districts, vehicles unlikely 


10 


12.0 


2b 


12.0 



246 
Copyright © 2001 IEEE. All rights reserved. 



APPENDIX A 



Table A-2b 
Reference Components of Rule 234 



Table 


Item 


Ref 
(mm/m) 


Rei 

(ft) 


234-1 


1. Buildings 




~\ 3.0 ■ : '■ 
3.0 

'"TTlo; ; ■■' 

8 
9:0 
9.0 

; .14.0. : 




a. Horizontal 






(1) Walls, projections, and guarded windows 


915 mm 




(2) Unguarded windows 


915 mm 




(3) Balconies and areas accessible to pedestrians 


915 mm 




b. Vertical 






(1) Roofs/projections not accessible to pedestrians 


2.44 m 




(2) Balconies and roofs accessible to pedestrians 


2.74 m 




(3) Roofs — vehicles not over 2.4 m (8 ft) 


2.74 m 




(4) Roofs — vehicles over 2.4 m (8 ft) 


4.3 m 




2. Signs, chimneys, billboards, antennas, tanks, etc. 




3,0 




a. Horizontal 


9.15 mm 




b. Vertical over or under 


1.07 m 


3.5 


234-2 


1 . Over bridges 








a. Attached 


305 mm 


:: : 1.0 . . 




b. Not attached 


2.44 m 


8.0 




2. Beside, under, or within bridge structure 








a. Accessible 








(1) Attached 


305 mm 


1.0 




(2) Not attached 


2.44 m 


3 




b. Inaccessible 








(1) Attached 


305 mm 


■ 




(2) Not attached 


610 mm 


■ 


234-3 


A. From water level, edge of pool, etc. 


6.25 m 


20,5 




B. From diving platform or tower 


3.8 m 


12.5 



I 



247 
Copyright © 2001 IEEE. All rights reserved. 



APPENDIX A 



| Application rules were revised in 1990 to coordinate with clearances developed under the component or 
building-block approach. 

Vertical clearances now apply at the maximum conductor sag condition, such as outlined in Rule 232A, 
rather than at a 15 °C (60 °F) conductor temperature condition as used in the 1987 Edition. This is illustrated 
in Fig A-l: 5.6 m (18.5 ft) is required for open supply conductors, over 750 V to 22 kV, over roads, for any 
sag condition or span length. 

1990 METHOD 

MAXIMUM SAG CONDITION 

(50 °C [120 °F], MAXIMUM TEMPERATURE 

IF GREATER, OR ICE) 



I 



4.3 m 



REFERENCE 
COMPONENT(i4ft) 




MECHANICAL AND 
ELECTRICAL COMPONENT 



CLEARANCE 



ANY SPAN 



CONDITION— CLEARANCE OF OPEN SUPPLY CONDUCTORS, 750 V-22 kV, ABOVE ROADS 
CLEARANCE (5.6 m [18.5 ft])= REFERENCE COMPONENT (4.3 m [14 ft]) 
+ MECHANICAL AND ELECTRICAL COMPONENT (1 .37 m [4.5 ft]) 

Fig A-l 
Clearance at Maximum Sag 



Not only is the intended vertical clearance shown, rule simplification is also achieved. Rules for long-span 
construction and/or high-temperature operation were removed because they are no longer necessary. 

Horizontal clearances to buildings and other installations now apply with the conductor at rest (no wind 
displacement) as outlined in Rule 234A, rather than at a wind displacement condition. The horizontal clear- 
ance for open supply conductors from buildings (over 750 V to 22 kV) at rest is now 2.3 m (7.5 ft) (Table 234- 
1). This clearance is essentially the same as the 2.44 m (8 ft) required by early code editions. 

Wind displacement need be considered only for energized open supply conductors and 230C2-230C3 ca- 
bles energized at more than 750 V; see Rule 234C1. In the above example, a minimum clearance of 1.37 m 
(4.5 ft) is required under wind displacement conditions. While less than the 1.5 or 1.8 m (5 or 6 ft) required 
under prior codes, people will not be working on outside building walls during high wind conditions. 

Because application rules have been revised, it must be understood that clearance values cannot be direct- 
ly compared between the 1987 and 1990, 1993, or 1997 Editions. Vertical clearance values appear smaller 
because sag changes formerly included in clearance values are now addressed in the application rules. Hori- 
zontal clearance values appear larger because wind displacement is now applicable to energized conductors 
and certain supply cables only; clearances for all wires, conductors, and cables are shown in the tables under 
at-rest conditions. 

The following changes were also made to consolidate requirements and simplify application: 

248 
Copyright © 2001 IEEE. All rights reserved. 



APPENDIX A 

• Voltages in the tables are limited to V to 750 V and over 750 V to 22 kV, normal secondary and 
primary distribution ranges respectively. Voltages in the 22 kV to 50 kV range are covered by a 10 mm- 
per-kV (0.4-in-per-kV) adder; see Rules 232Cla, 232C2a, and 234G1. Exceptions at 22 kV to 50 kV 
are noted where they apply. 

• Rules for voltages above 22 kV and the alternate clearances for voltages above 98 kV are consolidated. 

• Clearances for equipment cases are relocated from Rules 286E and 286F to Rules 232B3 and 234J. 

Clearance Rules and Tables Prior to 1990 

In editions prior to 1990, clearances shown in the tables were basic clearances, applied under specified 
conditions of conductor temperature and sag, span length, and voltage range. For example, vertical clearances 
in Table 232-1 of the 1987 Edition applied at a conductor temperature of 15 °C (60 °F), no wind, final un- 
loaded sag. Span lengths were limited by loading district. Voltages up to 50 kV were covered in the table. 
Conditions outside these basic conditions required additional clearances. 

Actual clearances vary from the values required at 15 °C (60 °F) as conductor sag changes due to 
conductor movement under loading. Table 232-1 allowed 610 mm (24 in) for ice loading, higher conductor 
temperatures [to 50 °C (120 °F)], and structure flexure. The actual allowance was 460 mm (18 in) for ice 
loading or higher conductor temperature plus 152 mm (6 in) for miscellaneous causes. Thus, the true 
clearance requirement was 610 mm (24 in) less than the value shown in the table (i.e., equivalent to the 
clearance required for rigid parts). 

Table 232-2, vertical clearance of rigid live parts, was consistent with the 610 mm (24 in) allowance in 
Table 232-1. A rigid live part energized at 750 V to 22 kV over a road (item la, middle column) required a 
5.5 m (18 ft) clearance. A conductor energized at the same voltage over a road required a 6.1 m (20 ft) clear- 
ance (Table 232-1, item 2). The additional 610 mm (24 in) was the allowance for conductor movement, and 
the true clearance that may be experienced is 5.5 m (18 ft) — the same as specified for rigid live parts. 

Additional clearances above the basic values shown in Table 232-1 were required when the limiting 
conditions were exceeded. Rule 232B2c covered long-span construction and Rule 232B2d covered high- 
temperature operation. Both rules recognized and allowed for additional conductor movement. Finally, Rule 
232B1 required additional clearance for voltages exceeding 50 kV. Note that this was an electrical 
requirement apart from conductor movement. 

Application of basic and additional clearances is illustrated in the drawings that follow. 

Fig A-2 shows the basic clearance applied at a 15 °C (60 °F) conductor temperature, at the limiting span 
length. When conductor movement is considered, the actual clearance at maximum sag is less than the basic 
clearance. 

Fig A-3 shows application of an additional clearance for conductor temperature over 50 °C (120 °F), at the 
limiting span. Note that the additional clearance is added to the basic clearance to determine the required 
clearance. Again, the actual clearance at maximum sag is essentially the same as in Fig Al. 

Fig A-4 shows application of a long-span additional clearance, for a conductor operating at or within the 
50 °C (120 °F) limit. As before, the additional clearance is added to the basic clearance, and the actual con- 
ductor clearance at maximum sag is essentially the same as in Fig A-2. 

To repeat, both the basic clearances shown in the tables and the additional clearances required by the 
rules apply only when the conductor temperature is 15 °C (60 °F). Actual clearances are expected and 
intended to be less due to conductor movement. Only the voltage adder (for voltages above those shown 
in the tables) is a true clearance requirement. 

249 
Copyright © 2001 IEEE. All rights reserved. 



I 



APPENDIX A 



PRIOR METHOD 



BASIC CLEARANCE 



SAG CHANGE 460 mm , 

I (18 in) f 



L t 



150 mm CONDUCTOR FACTOR 
(6 in) 



15 °C CONDITION 
(60 °F) 




5.5 m RIGID 
(18 ft) LIVE 



6.1 m BASIC CLEARANCE 
(20 ft) 



PART 
CLEARANCE 



MAXIMUM SAG 

CONDITION 

(50°C[120°F]ORICE) 



LIMITING SPAN 



CONDITION— CLEARANCE OF OPEN SUPPLY CONDUCTORS, 750 V-22 kV, ABOVE ROADS 

LIMITING SPAN— 53.3 m (175 ft) MAXIMUM IN HEAVY LOADING DISTRICT 

,,,,,,, .—CONDUCTOR MOVEMENT 

BASIC CLEARANCE (6.1 m [20 ft]) = ACTUAL CLEARANCE (5.5 m [18 ft]) + CONDUCTOR 
MOVEMENT 0.6 m (2 ft) 

Fig A-2 
Basic Clearance 



250 
Copyright © 2001 IEEE. All rights reserved. 



APPENDIX A 



PRIOR METHOD 



HIGH TEMPERATURE OPERATION (ABOVE 50 °C [120 °F[) 



ADDITIONAL CLEARANCE REQUIRED 
FOR HIGH TEMPERATURE OPERATION 



1 5 °C (60 °F) CONDITION 



CONDUCTOR ATTACHMENT 
POINT FOR HIGH 
TEMPERATURE OPERATION (H2) 



CONDUCTOR ATTACHMENT 
POINT IF CONDUCTOR 
TEMPERATURE LIMITED 
TO 50 °C(120°F) (AS IN 
FIG1)(H1) 




5.5 m RIGID 

M«m LIVE 
(18ft) PART 

CLEARANCE 



6.1 m 
(20 ft) 



BASIC CLEARANCE 



HIGH TEMPERATURE 
CONDITION 



LIMITING SPAN 



NDITION— CLEARANCE OF OPEN SUPPLY CONDUCTORS, 750 V-22 kV, ABOVE ROADS 
, , s , ,— CONDUCTOR MOVEMENT 
—POSITION OF CONDUCTOR FOR BASIC CLEARANCE CONDITION (FIG 1) 

UIRED CLEARANCE (@ 15 °C [60 °F]) = BASIC CLEARANCE (6.1 m [20 ft]) + ADDITIONAL CLEARANCE REQUIRED FOR 
H TEMPERATURE OPERATION (ABOVE 50 °C [120 °F]) 



Fig A-3 
Additional Clearance Required for High-Temperature Operation 



I 



251 
Copyright © 2001 IEEE. All rights reserved. 



APPENDIX A 



LONG SPAN CONSTRUCTION 



Prior Method 




MAXIMUM SAG 
CONDITION 
50 °C OR ICE 
[120 °F OR ICE) 



CONDITION— CLEARANCE OF OPEN SUPPLY CONDUCTORS, 750 V-22 kV, ABOVE ROADS 

f s , , , , , — CONDUCTOR MOVEMENT 

—POSITION OF CONDUCTOR FOR BASIC CLEARANCE CONDITION (FIG 1) 

REQUIRED CLEARANCE (@ 15 °C [60 °F]) = BASIC CLEARANCE (6.1 m [20 ft]) + ADDITIONAL CLEARANCE REQUIRED FOR 
LONG SPAN CONSTRUCTION (ASSUMING MAXIMUM CONDUCTOR TEMPERATURE LIMITED TO 50 °C [120 °F]) 

Fig A-4 
Additional Clearance Required for Long-Span Construction 



252 
Copyright ©2001 IEEE. All rights reserved. 



APPENDIX A 



Clearance Values Prior to 1990 

Clearance values were based on experience. They were developed over time, at different times, for differ- 
ent reasons. 

While those clearance values worked well, partly because several of them proved to be overly 
conservative, they did not follow a uniform system. For example, Table 234-1 showed vertical clearances 
from buildings. In line lb(l) of the 1987 Edition, vertical clearance of open supply conductors over roofs not 
accessible to pedestrians was the same for all voltages from to 22 kV. However, in line lb(3), the vertical 
clearance of open supply conductors over roofs accessible to vehicles but not subject to truck traffic varied 
with voltage: 3.6 m (12 ft) for conductors energized at V to 300 V, 4.6 m (15 ft) for 300 V to 750 V, and 
6.1 m (20 ft) for 750 V to 22 kV. 

Summary — Prior Editions 

The clearance section was complex, with requirements stated in design manual format. Clearance was a 
mixture of basic clearance, clearance to cover conductor movement, and voltage clearance. Required 
clearance applied only at a 15 °C (60 °F) conductor temperature; actual clearance was not shown. Finally, 
clearance values were empirical; they were not systematized. 

Clearances Subcommittee Activities 

Subcommittee 4 discussed problems with the clearance section of the code during the 1987 revision cycle. 
Because there was insufficient time to develop a comprehensive proposal, Subcommittee 4 recommended 
formation of a special working group. The NESC Committee approved this recommendation and established 
Working Group 4.2 to: 

• Review overhead line clearances, primarily Rules 232 and 234 and Section 28, and 

• Investigate feasibility of a uniform method of determining clearances under all conditions of conductor 
movement. 

The working group concluded that: 

• A uniform system for determining clearances could be developed utilizing a building-block approach. 

• Vertical clearance values could be stated for maximum sag conditions to cover conductor movement. 

• Horizontal clearances could be stated under at-rest conditions, with special requirements to cover dis- 
placement of energized conductors during wind conditions. 

• The revisions proposed in the working group report were explicit, readily understood, and performance 
oriented. 

Subcommittee 4 reviewed and approved the Working Group 4.2 report with minor modifications. Further 
enhancements were made in response to public comment. 

Summary 

| The 1990 changes constitute a comprehensive revision of Section 23, which incorporates related provi- 
sions of Section 28 and provides significant user benefits, as detailed in the introduction at the beginning of 
this discussion. While some clearance values may appear to be larger and some smaller, the net effective 
clearances for energized conductors and cables are essentially unchanged. 



I 



253 
Copyright ©2001 IEEE. All rights reserved. 



APPENDIX B 



Bibliography 

[Bl] ANSI A14.1-1994, American National Standard Safety Requirements for Portable Wood Ladders. [Rule 323F 
REC] 

[B2] ANSI A14.2-1990, American National Standard Safety Requirements for Portable Metal Ladders [and supple- 
ment ANSI 14.2a (1985)]. [Rule 323F REC] 

[B3] ANSI A14.3-1992, American National Standard Safety Requirements for Fixed Ladders. [Rule 323F REC] 

[B4] ANSI A14.5-1992, American National Standard Safety Requirements for Portable Reinforced Plastic Ladders 
[and supplement ANSI A14.5a (1985)]. [Rule 323F REC] 

[B5] ANSI A1264. 1-1995, American National Safety Requirements for Workplace Floor and Wall Openings. [Rule 
112 D NOTE] 

[B6] ANSI C2-1973, National Electrical Safety Code. [Rule 402 NOTE] 

[B7] ANSI C29.9-1983, American National Standard for Apparatus, Post Type Wet-Process Porcelain Insulators. 
[Rule 277 NOTE 2] 

[B8] ANSI C29.1 1-1989, American National Standard Tests to Composite Suspension Insulation for Overhead 
Transmission Lines. [Rule 277 NOTE lb] 

[B9] API RP 500, Recommended Practice for Classification of Locations for Electrical Installations at Petroleum 
Facilities, 1 June 1991. [Rule 127LNOTE] 

[BIO] ASTM F 478-92, Standard Specification for In-Service Care of Insulating Line Hose and Covers. 

[Bll] ASTM F 479-95, Standard Specification for In-Service Care of Insulating Blankets. 

[B 12] ASTM F 496-96, Standard Specification for In-Service Care of Insulating Gloves and Sleeves. 

[B13] ASTM F 696-91, Standard Specification for Leather Protectors for Rubber Insulating Gloves and Mittens. 

[B 14] ASTM F 71 1-89, Standard Specification for Fiberglass-Reinforced Plastic (FRP) Rod and Tube Used in Live 
Line Tools. 

[B15] ASTM F 855-96, Standard Specification for Temporary Grounding Systems to Be Used on De-energized Elec- 
tric Power Lines and Equipment. 

[B16] ASTM F 887-91a, Standard Specification for Personal Climbing Equipment. 

[B17] ASTM F 914-91, Standard Test Method for Acoustic Emission for Insulated Aerial Personnel Devices. 

[B18] ASTM F 968-93, Standard Specification for Electrically Insulating Plastic Guard Equipment for Protection of 
Workers. 

[B19] ASTM F 1 1 16-88 (1995), Standard Test Method for Determining Dielectric Strength of Overshoe Footwear. 

[B20] ASTM F 1236-96, Standard Guide for Visual Inspection of Electrical Protective Rubber Products. 

[B21] IEEE/ASTM SI 10-1997, Standard for the Use of the International System of Units (SI). [Rule 17A, 
Footnote 2] 

254 
Copyright © 2001 IEEE. All rights reserved. 



APPENDIX B 

[B22] IEEE Std 80-2000, IEEE Guide for Safety in AC Substation Grounding. [Rule 96A NOTE and Rule 123B 
NOTE] 

[B23] IEEE Std 268-1992, IEEE Standard for Metric Practice (ANSI) (DoD adopted). 

[B24] IEEE Std 524-1992, IEEE Guide to the Installation of Overhead Transmission Line Conductors (ANSI). 

[B25] IEEE Std 738-1993, IEEE Standard for Calculating the Current-Temperature of Bare Overhead Conductors 
(ANSI). 

[B26] IEEE Std 751-1990, IEEE Trial-Use Design Guide for Wood Transmission Structures (ANSI). 

[B27] IEEE Std 935-1989 (R1995), IEEE Guide on Terminology for Tools and Equipment to Be Used in Live Line 
Working (ANSI). 

[B28] IEEE Std 951-1996, IEEE Guide to the Assembly and Erection of Metal Transmission Structures (ANSI). 

[B29] IEEE Std 957-1995, IEEE Guide for Cleaning Insulators (ANSI). 

[B30] IEEE Std 977-1991, IEEE Guide to Installation of Foundations for Transmission Line Structures (ANSI). 

[B31] IEEE Std 978-1984 (R1990), IEEE Guide for In-Service Maintenance and Electrical Testing of Live-Line 
Tools (ANSI). 



[B32] IEEE Std 987-1985, IEEE Guide for Application of Composite Insulators (ANSI) 



12 



[B33] IEEE Std 1024-1988, IEEE Recommended Practice for Specifying Distribution Composite Insulators (Suspen- 
sion Type) (ANSI). 13 

[B34] IEEE Std 1048-1990, IEEE Guide for Protective Grounding of Power Lines (ANSI). 

[B35] IEEE Std 1067-1996, IEEE Guide for In-Service Use, Care, Maintenance, and Testing of Conductive Clothing 
for Use on Voltages up to 765 kV AC (ANSI). 

[B36] IEEE Std 1070-1988, IEEE Guide for the Design and Testing of Transmission Modular Restoration Structure 
Components (ANSI). 

[B37] IEEE Std 1 1 19-1988 (R1993), IEEE Guide for Fence Safety Clearances in Electric-Supply Stations (ANSI). 

[B38] IEEE Std C62. 1-1989 (R1994), IEEE Standard for Gapped Silicon-Carbide Surge Arresters for AC Power Cir- 
cuits (ANSI). [Rule 190 NOTE] 

[B39] IEEE Std C62.1 1-1999, IEEE Standard for Metal-Oxide Surge Arresters for Alternating Current Power Cir- 
cuits (ANSI). [Rule 190 NOTE] 

[B40] IEEE Working Group on Switching Surges, "Switching Surges, pt. IV — Control on AC Transmission Lines," 
IEEE Transactions on Power Apparatus and Systems, vol. PAS-101, No. 8, pp. 2694-2702, Aug. 1982. 

[B41] NFPA 77-1993, Recommended Practice on Static Electricity. [Rule 127D3 NOTE] 



12 IEEE Std 987-1985 has been withdrawn; however, copies can be obtained from Global Engineering, 15 Inverness Way East, Englewood, CO 

80112-5704, USA, tel. (303) 792-2181. 

13 IEEE Std 1024-1988 has been withdrawn; however, copies can be obtained from Global Engineering. 

255 
Copyright © 2001 IEEE. All rights reserved. 



I 



APPENDIX B 



[B42] NFPA 497M-1991, Classification of Gases, Vapors, and Dusts for Electrical Equipment in Hazardous (Classi- 
fied) Locations. [Rule 127L NOTE] 

[B43] OSHA 29 CFR 1926 Subpart V— Power Transmission and Distribution. [Rule 402 NOTE] 

[B44] OSHA Federal Register [01/31/89] 54: 4974-5024 — Electric Power Generation, Transmission, and Distribu- 
tion; Electrical Protective Equipment; Proposed Rule (1910.269). [Rule 402 NOTE] 

[B45] OSHA Federal Register [01/31/94] 59: 4320-4476— Electric Power Generation, Transmission, and Distribu- 
tion; Electrical Protective Equipment (1910.269). [Rule 402 NOTE] 



256 
Copyright © 2001 IEEE. All rights reserved. 



Index 



Italic type is used for C2 rule, section, part, figure, or table identification. The corresponding page numbers follow 
in upright type. 



Adjustable-speed motors, 130E; 49 

Administrative authority, definition of, Sec. 2; 4 

Aerial cable systems, insulation requirements, 278; 
186 

Aerial services, 239G4; 151 

Altitude corrections (for approach distance to live 
parts), 431, 441A5, Table 441-5; 222, 225, 232 

American Wire Gage (AWG), Sec. 2; 13 

Ampacity 

Definition of, Sec. 2; 4 
Grounding conductor, 93 C; 19 

Anchorage, definition of, Sec. 2; 4 

Anchors, 253, 261 B; 170, 175 

Annunciators, 180E; 56 

Antennas, conductor clearance from, 234C, 

Table 234-1, Table 234-5, 2351; 99, 102, 121, 141 

Apparent sag at any point in a span, definition of, 

Sec. 2; 10 

Apparent sag of a span, definition, Sec. 2; 10 

Application of National Electrical Safety Code, 

013; 1 

Approach distance 

Live parts, 441 A; 224 
Minimum, definition of, Sec. 2; 8 

Arcing, 420F, 447; 217, 240 

Armless construction, 24 3 C, 261G; 160, 177 

Augers (grain bins), clearance considerations, 234F, 
Fig 234-4; 114, 115 



Authority, administrative, definition of, Sec. 2; 4 
Automatic, definition of, Sec. 2; 4 

Automatic overspeed trip device for prime movers, 

BOA; 49 

AWG (American Wire Gage), Sec. 2; 13 

B 

Backfill, 321B; 193 
Definition of, Sec. 2; 4 

Ballast section (railroads), definition of, Sec. 2; 4 

Basic Impulse Insulation Level (BIL), Table 124-1; 37 

Batteries. See Storage batteries 

Beaches, conductor clearance from, 234E2; 109 

Belt (line-worker's body), Sec. 2, 420K; 6, 201 

B grade construction. See Grades of construction 

BIL (Basic Impulse Insulation Level), Table 124-1; 37 

Billboards, conductor clearance from, 234C, 
Table 234-1; 99, 102 

Birmingham Wire Gage, Sec. 2; 13 

Boilers, 127F, 180E1; 47, 56 

Bonding, definition of, Sec. 2; 4 

Bonding jumpers, buried, 92E, 93E6b; 18, 21 

Boring, 352C; 204 

Braces for line supports, 261D; 176 

Breaker, circuit. See Circuit breakers 



I 



257 
Copyright © 2001 IEEE. All rights reserved. 



INDEX 



Bridges 

Clearance from, 234; 96 
Conduit location, 320A4; 192 
Trolley guards under, 225E; 68 

Brown & Sharpe (B&S), Sec. 2; 13 

Buckarm construction, 236F, 237D, Fig 237-1; 
144, 146 

Buildings, clearance from, 234, Fig 234-1, 

Table 234-1, Table 234-4; 96, 97, 101, 120 
Buried cable under, 351C2; 203 

Bundled conductors, definition of, Sec. 2; 5 

Buried lines. See Underground communication lines; 
Underground electric supply lines 

Burner safety devices, 180E; 56 

Bus, metal-enclosed, 181; 56 
Isolated-phase, 181B; 56 



Cable jacket, definition of, Sec. 2; 4 

Cables 

Aerial, insulation requirements, 278; 186 
Communication, 261K; 178 
Definition of, Sec. 2; 4 
Fiber-optic — communication 

Clearances, 230F; 70 

Definition of, Sec. 2; 6 
Fiber-optic — supply 

Clearances, 230F; 70 

Definition of, Sec. 2; 6 
Fireproofing, definition of, Sec. 2; 6 
Insulation, definition of, Sec. 2; 7 
Spacer, definition of, Sec. 2; 1 1 
Supply, 230C, 241A; 69,155 

Cable sheath, definition of, Sec. 2; 4 

Cable terminal, definition of, Sec. 2; 4 

Capacitors, 4431; 236 

C grade construction. See Grades of construction 

Chimneys, conductor clearance from, 234C, 
Table 234-1, Table 234-5; 99, 102, 121 



Circuit 

Definition of, Sec. 2; 4 

Voltage in, definitions of, Sec. 2; 12 

Circuit breakers 

Application, 777; 54 

Arrangement, 770; 54 

Capacity, 173 A; 54 

Definition of, Sec. 2; 4 

Oil-containing, 772; 54 

Provisions for disconnecting, 173B; 54 

Visible break switch, 773C; 54 

Classified locations, electrical installations in 

Boilers, 7277; 180E1; 47, 56 

Coal-handling areas, 727A; 46 

Flammable and combustible liquids, 7277?; 46 

Loading and unloading facilities, 7277); 47 

Storage areas, 727C; 47 
Gaseous hydrogen systems for supply equipment, 

727G; 47 
Gasoline-dispensing stations, 7277?; 47 
Liquid hydrogen systems, 127H; 48 
Liquid petroleum gas (LPG), 7277C 48 
Loading and unloading facilities, 727D; 47 
Natural gas (methane), 727L; 48 
Sulfur, 7277; 48 

Clearance. See Overhead communication lines, 
clearances; Overhead electric supply lines, 
clearances 

Climbable, readily, definition of, Sec. 2; 9 

Climber, qualified, Sec. 2, 420K2; 9, 217 

Climbing, definition of, Sec. 2; 4 

Climbing space, 230A; 69 
Buckarm construction on, 236F; 144 
Conductors bounding, 236E, Table 236-1; 142 
Dimensions, 236A; 141 
Equipment location in relation to, 236D; 142 
Inhibiting climbing of supporting structures, 217A2; 

62 
Lateral conductors, past, 239B; 149 
Location, 236A; 141 
Longitudinal runs not on support arms, past, 236G; 

144 
Portions of supporting structures in, 236B; 141 
Ridge-pin conductors near, 2361; 144 
Steps and standoff brackets for supporting structures, 

217A2; 62 
Support arm location relative to, 236C; 141 
Vertical conductors, past, 236H, 239B; 144, 149 



258 
Copyright © 2001 IEEE. All rights reserved. 



INDEX 



Clothing, protective, 4201; 211 

Coal-handling areas, 127 A; 46 

Combustible liquids, 127B; 46 
Loading and unloading facilities, 127D; 41 
Storage areas, 127C; 47 

Common use, definition of, Sec. 2; 4 

Communication lines. See Lines, communication 

Communication worker safety zone, 235C4, 238E; 
133, 147 

Computers, 180E1; 56 

Concentric neutral cable as grounding electrode, 

94B5; 23 

Concrete-encased electrodes as ground electrodes, 

94B6, 95A; 23 

Concrete structures. See Prestressed-concrete 
structures; Reinforced concrete structures 

Conductors, Sec. 16; 53 

Application, 160; 53 

Bundled, definition of, Sec. 2; 5 

Clearance envelope, 233A2, Fig 233-1, Fig 233-3, 
Fig 234-4; S5, 86, 89, 115 

Climbing space bounding, 236E; 142 

Communication. See also Lines, communication 
Open-wire, 261 J; 178 
Paired, 261L; 178 

Constant-current, 242A; 156 

Covered, Sec. 2, 230D; 5, 70 

Definition of, Sec. 2; 5 

Electrical protection, 161; 53 
Grounded, 161B; 53 
Insulated power cables, 161 C; 53 
Overcurrent protection required, 161 A; 53 

Fastenings, 243C, 252, 261F; 160, 169, 177 

Fiber-optic, definition of, Sec. 2; 6 

Fire-alarm circuits, 242D; 156 

Grades of construction 
Communication conductors, 242C, Table 241-1, 

Table 242-2; 156, 157, 159 
Constant-current circuit conductors, 242A; 156 
Fire-alarm circuit conductors, 242D; 156 
Neutral conductors of supply circuits, 242E; 156 
Railway feeder conductors, 242B; 156 
Supply, 241A, Table 242-1; 155, 157 
Surge-protection wires, 242F; 156 
Trolley-contact circuit conductors, 242B; 156 



Grounded, 161B; 53 

Definition of, Sec. 2; 5 
Grounding. See Grounding, conductors 
Installing, 447; 240 
Insulated, 161C; 53 

Definition of, Sec. 2; 5 
Isolation, 163; 53 
Lateral, definition of, Sec. 2; 5 
Line. See Overhead communication lines; 

Overhead electric supply lines 
Loading, 251; 168 
Maintaining, 447; 240 
Mechanical protection and support, 162; 53 
Movement envelope, 233A1, Fig 233-1, Fig 233-2; 

85, 86, 87 
Neutral, Sec. 2, 230E, 242E; 8, 70, 156 
Open, Sec. 2, 261H; 5, 177 
Overcurrent protection required, 161 A; 53 
Railway feeder, 242B; 156 
Ridge pin, 2361; 144 
Sag, definition of, Sec. 2; 9 
Shielded, 92B2b; 16 
Shielding, definition of, Sec. 2; 5 
Spacing, 235G; 140 

Strength requirements. See Strength requirements 
Supply. See Overhead communication lines; 

Overhead electric supply lines 
Surge-protection, 242 F; 156 
Terminations 
Insulation, 164A; 53 

Metal-sheathed or shielded cable, 164B; 53 
Trolley-contact circuit, 225 A, 234A3, 234D2, 239G, 

241C3b, 242B, 243, 261H3; 67, 96, 109, 150, 

155, 156, 160, 178 
Voltage to ground, definition of, Sec. 2; 13 

Conduit 

Definition of, Sec. 2, Sec. 32; 5, 192 
Multiple duct, Sec. 2; 5 
Single duct, Sec. 2; 5 

Conduit systems, definition of, Sec. 2; 5 

Conflict 

Between lines, avoidance of, 221; 65 
Structure, definition of, Sec. 2; 1 1 

Constant-current circuit, voltage of (definition), Sec. 

2; 12 

Control, motor, 130, 131, 180D; 49, 56 
Control switchboards, 180E; 56 

Conveyors (grain bins), clearance considerations, 

234F, Fig 234-4; 114,115 



I 



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INDEX 



Cover, manhole, definition of, Sec. 2; 8 

Covered conductors, 230D; 70 
Definition of, Sec. 2; 5 

Crossarms for line supports. See also Supporting 
structures 
Grades of construction, 243B, 263C; 160, 181 
Loads upon, 252, 253; 169, 170 
Strength, determining, 26 ID; 176 

Crossings, 225D, 241C; 67, 155 

Current-carrying part, definition of, Sec. 2; 5 

Current transformers, 150; 51. See also Transformers 

Cylindrical structures and components, 2 52 B 2a; 169 

D 

DC. See Direct current systems 
Deadends, 252C3, 261Flc; 170, 177 
Dead-front power switchboards, 180C; 56 
Decorative lighting, 217A5; 63 
De-energized, definition of, Sec. 2; 5 

De-energizing lines and equipment, 444; 237 

Definitions of National Electrical Safety Code terms, 

Sec. 2; 4 

Designated person, definition of, Sec. 2; 5 
Diagonal clearance, 235D; 133 

Direct current systems 

Clearances, 230G; 70 
Grounding methods, 123D; 35 
Grounding point, 92 A; 16 
Disconnecting switch, Sec. 17; 54 
Definition of, Sec. 2; 5 

Districts 

Rural, definition of, Sec. 2; 9 
Urban, definition of, Sec. 2; 12 

Drop, service, definition of, Sec. 2; 10 

Ducts, 322; 193 
Definition of, Sec. 2, Sec. 32; 5, 192 
Installation, 322B; 194 



E 



Effective date of National Electrical Safety Code, 

016; 3 

Effectively grounded, definition of, Sec. 2; 6 

Effectively grounded circuits, voltage of (definition), 

Sec. 2; 12 

Electrical code. See National Electrical Code; National 
Electrical Safety Code 

Electric railway construction, 225; 67. See also 
Railroads 
Guards under bridges, 225E; 68 
High-voltage contact conductors, 225B; 67 
Prevention of contact loss at railroad crossings at 

grade, 225D; 67 
Third rails, 225C; 67 
Trolley-contact conductors, 225A, 234A3, 234D2, 

239G, 241C3b, 242B, 243, 261H3; 67, 96, 109, 

150, 155, 156, 160, 178 

Electric supply equipment, definition of, Sec. 2; 6 

Electric supply lines. See Lines, electric supply 

Electric supply stations. See Supply stations, electric 

Electric supply systems, operation of. See Operation 
of electric supply systems, employee rules; 
Operation of electric supply systems, employer 
rules 

Electrodes, grounding. See Grounding, electrodes 

Electron-tube-containing devices, 180E; 56 

Elevation 

Correction for approach distance to live parts, 441 A5, 

Table 441-5; 225, 232 
Isolated by, definition of, Sec. 2; 7 

Elevators, grain, clearance considerations, 234F, 
Fig 234-4; 114, 115 

Emergency installations, 014A; 2 
Clearances for, 230A2; 69 
Inspections, 121 C; 34 

Emergency lighting, supply station, 11 IB; 30 



260 
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INDEX 



Emergency procedures, 410B; 214 

Employee rules. See Operation of electric supply 
systems, employee rules 

Employer rules. See Operation of electric supply 
systems, employer rules 

Enclosed, definition of, Sec. 2; 6 

Enclosure of equipment, 110A, 124C2; 28, 35 

Energized 

Definition of, Sec. 2; 6 
Equipment 
Guarding, 237E; 146 
Working on. See Operation of electric supply 

systems, employee rules, energized lines and 
equipment 
Parts, equipment for work on, 126, 446B; 46, 239 

Envelope, clearance, 233A2, Fig 233-1, Fig 233-3, 
Fig 234-4; %5, 86, 89, 115 

Equipment 

Cases, 23432; 118 

Clearance, 234 J; 118. See also Overhead 

communication lines, clearance; Overhead 
electric supply lines, clearance 
Climbing space, location relative to, 236D; 142 
Definition of, Sec. 2; 6 
Electric supply. See Supply stations, electric 
Grounding conductors for, 93C5; 19 
Installation. See Installation and maintenance of 

equipment 
Maintenance. See Installation and maintenance of 

equipment 
Remotely operable, definition of, Sec. 2; 9 
Rotating. See Rotating equipment 
Underground, Sec. 38; 210 

Design, 381; 210 

Grounding, 384; 211 

Identification, 385; 211 

Installation, 383; 21 1 

Location, 382; 211 
Utilization, definition of, Sec. 2; 12 

Excavation, 321A, 423D; 193, 221 

Existing installations, 013B; 2 

Exits, supply station, 113; 33 

Exposed, definition of, Sec. 2; 6 



Extension of installations, 013A; 1 

F 

Fall arrest system, definition of, Sec. 2; 6 

Fall prevention system, definition of, Sec. 2; 6 

Fall protection, 41 IF, 420K; 215, 217 

Fall protection program, definition of, Sec. 2; 6 

Fall protection system (hardware), Sec. 2, 420K; 6, 
217 

Fastenings, conductor, 243C, 252, 261F; 160, 169, 177 

Fences 

Grounding of, 93E, 93C6; 18, 19 

Safety clearance zone, 110A2, Fig 110-1; 28, 29 

Types of, 110A1; 28 

Fiber-optic cable — communication 

Clearances, 230F; 70 
Definition of, Sec. 2; 6 

Fiber-optic cable — supply 

Clearances, 230F; 70 
Definition of, Sec. 2; 6 

Fiber-optic conductor, definition of, Sec. 2; 5 

Fiber stress, wood, 261A2; 174 

Final sag, definition of, Sec. 2; 10 

Final unloaded sag, definition of, Sec. 2; 10 

Final unloaded tension, definition of, Sec. 2; 12 

Fire-alarm circuit conductors, 242D; 156 

Fire-extinguishing equipment, 114, 420L; 33, 218 

Fire hydrants, clearances from, 231 A; 71 

Fireproofing (of cables), definition of, Sec. 2; 6 

First aid rules, 410B; 214 

Flammable liquids, 127B; 46 
Loading and unloading facilities, 127D; 47 
Storage areas, 127C; 47 



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Flashover voltage, insulation, 272; 185 

Flat-surfaced structures and components, 252B2b; 
169 

Floors, supply station, 112A; 32 

Foundations, loads upon, 252, 253, 261B; 169, 170, 
175 

Fuel lines, separation from underground conduit, 

320B5; 193 

Fuses, Sec. 17, 420N; 54, 218 
Application, 171; 54 
Arrangement, 170; 54 
Capacity, 173 A; 54 
Disconnecting, 173B, 174; 54 
Visible-break, 173C; 54 



G 



Gages, wire, definition of, Sec. 2; 13 

Gaseous hydrogen systems for supply equipment, 

127G; 47 

Gas-insulated equipment, 443 J; 236 

Gas lines, separation from underground conduit, 

320B5; 193 

Gasoline-dispensing stations, 127 E; 47 

Gates, 92E; 18 

Generating station, definition of, Sec. 2; 6 

Generators, Sec. 13; 49 
Motor control, 131; 49 
Short-circuit protection, 133; 49 
Speed control and stopping devices, 130; 49 

Grades of construction 

Application, 241; 155 

BandC 
Loading. See Loading, line 
Strength requirements. See Strength requirements 

Conductors 
Communication conductors, 242C, Table 242-1, 

Table 242-2; 156, 157, 159 
Constant-current circuit conductors, 242A; 156 
Fire-alarm circuit conductors, 242D; 156 
Neutral conductors of supply circuits, 242E; 156 



Railway feeder conductors, 242E; 156 

Supply, 241 A, Table 242-1; 155, 157 

Surge-protection wires, 242F; 156 

Trolley-contact circuit conductors, 242B; 156 
Crossings, 241C; 155 
Line supports, 243; 160 

Armless construction brackets, 243C; 160 

Conductor construction grade, change in, 252C1; 
169 

Conductor fastenings, 234C; 160 

Crossarms, 243B; 160 

Insulators, 243C; 160 

Pins, 243C; 160 

Structures, 243A; 160 

Support arms, 243B; 160 
N, strength requirements. See Strength requirements 
Order of grades, 241B; 155 

Grain bins, conductor clearance from, 234F, 
Fig 234-4; 114, 115 

Grating, manhole, definition of, Sec. 2; 8 

Ground, clearances above, 231B, 232, Table 232-1, 
Table 232-2; 71, 74, 81. See also Overhead 
communication lines, clearances; Overhead 
electric supply lines, clearances 

Grounded, definition of, Sec. 2; 7 

Grounded, effectively, definition of, Sec. 2; 6 

Grounded circuit, voltage of (definitions), Sec. 2; 12 

Grounded conductor, 161B; 53 
Definition of, Sec. 2; 5 

Grounded system, definition of, Sec. 2; 7 

Grounding 

Circuits and equipment, underground, 314; 190 
Communication lines, 99, 315; 26, 191 
Conductors, 215B; 61 

Ampacity, 93C; 19 

Common, for circuits and equipment, 93 F; 21 

Composition of, 93 A; 18 

Connection methods, 93, 95; 18, 23 

Connection points, 92, 95B; 16, 24 

Current in, 92D; 17 

Definition of, Sec. 2; 5 

Guarding, 93D; 20 

Protection, 93D; 20 

Separate, 92B3; 17 

Separation of, 97; 25 

Strength, 93C; 19 

Underground, 93E; 20 



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Direct current systems, 123D; 35 
Electrodes, 94, 99; 21, 26 

Existing, 94 A; 21 

Made, 94B; 21 
Equipment, 93C5, 123; 19, 34 

During maintenance, 123C; 35 
Guys, 92C, 93C5, 215C2; 17, 19 
Messenger wires, P2C, 93C5; 17, 19 
Purpose of code, 90; 16 
Resistance requirements, 96; 24 

Multi-grounded systems, 96C; 24 

Single-grounded systems, 96B; 24 

Supply stations, 96A; 24 
Scope of code, 91; 24 
Supporting structures, 215C1; 61 

Ground wire, definition of, Sec. 2; 10 

Guarded, definition of, Sec. 2; 1 

Guarding 

Definition of, Sec. 2; 1 

Grounding conductors, 93D, 239D; 20, 149 

Live parts, 124, 237E; 35, 146 

Strength of guards, 124B; 35 

Transmission machinery and suddenly moving 
parts, 122; 34 

Types of guards, 124C; 35 

Where required, 124A; 35 

Guys 

Anchors, 253, 261B; 170, 175 

Grounding, 92C, 93C5, 215C2; 17, 19, 61 

Insulators, 261C, 279A; 175, 187 

Overload factors, 253; 170 

Side guys, 261A3; 175 

Strength of, 261 C, 263B; 175, 183 



H 



Handhole. See Manholes, handholes, and vaults 

Harness, 420K; 111 
Definition of, Sec. 2; 1 

Highways. See also Roadways 

Limited access, definition of, Sec. 2; 8 

Horizontal clearance, 233B, 234A2, 234Clb, 234D1; 
89, 96, 99, 107 
Between line conductors, 235B, Table 235-1, Table 

235-2, Table 235-3; 121, 123, 124, 125 
From live parts, Fig 124-1, Table 124-1; 36, 37 



Horizontal loading component, 251B2; 168 

Hydrogen systems 

Gaseous, for supply equipment, 127G; 47 
Liquid, 127H; 48 
Mobile, 129; 48 



Ice. See Loading, line 

Identification, 128, 411E, 423E; 48, 215, 221 

Idle equipment, inspection of, 12 IB; 34 

Illumination 

Attachment plugs and receptacles, HID; 30 

Battery areas, 145; 50 

Decorative, 217A5; 63 

Emergency lighting, 11 IB; 30 

Fixtures, 111C; 30 

Levels, Table 111-1; 31 

Receptacles in damp or wet locations, 11 IE; 30 

Street and area, 263H, 420P; 182, 219 

Supply stations, 111; 30 

Under normal conditions, 111 A; 30 

Inch-foot-pound system, 017 A; 3 

Indoor installations 

Power transformers and regulators, 152B; 51 
Surge arresters, 797; 58 

Initial unloaded sag, definition of, Sec. 2; 9 

Initial unloaded tension, definition of, Sec. 2; 12 

In service, definition of, Sec. 2; 7 

In-service equipment, inspection of, 121 A, 214A; 34, 
60 

Inspections, 121, 214; 34, 60 
Emergency equipment, 727C; 34 
Idle equipment, 121B; 34 

In-service lines and equipment, 121A, 214A; 34, 60 
lines, 214; 60 
New equipment, 12 ID; 34 
Out-of-service lines and equipment, 214B; 60 
Protective devices, 41 1C; 215 
Underground lines and equipment, 313; 190 

When in service, 313A; 190 

When out of service, 313B; 190 



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Installation and maintenance of equipment, Sec. 12; 

34 
Classified locations, 127; 46 

Boilers, 127F; 47 

Coal-handling areas, 127 A; 46 

Flammable and combustible liquids, 127B; 46 

Flammable liquid storage area, 127 C; 47 

Gaseous hydrogen systems for supply equipment, 
127G; 47 

Gasoline-dispensing stations, 127E; 47 

Liquefied petroleum gas (LPG), 127K; 48 

Liquid hydrogen systems, 127H; 48 

Loading and unloading facilities, 127D; 47 

Natural gas (methane), 127L; 48 

Sulfur, 1271; 48 
Emergency equipment, 121C; 34 
Energized parts, equipment for work on, 126; 46 
General requirements, 720; 34 
Guarding live parts, 124, 237E; 35, 146 

Strength of guards, 124B; 35 

Types of guards, 124C; 35 

Where required, 124A; 35 
Guarding shaft ends, pulleys, belts, and suddenly 

moving parts, 122; 34 
Identification, 128; 48 
Idle equipment, 121B; 34 
In-service equipment, 121 A; 34 
Inspections, 121; 34 
Mobile hydrogen equipment, 129; 48 
New equipment, 121D; 34 
Protective grounding, 123; 34 

During maintenance, 123C; 35 
Working space about electric equipment, 125; 45 

Installation and maintenance of overhead 
communication lines. See Overhead 
communication lines 

Installation and maintenance of overhead electric 
supply lines. See Overhead electric supply lines 

Installation and maintenance of underground 
communication lines. See Underground 
communication lines 

Installation and maintenance of underground 

electric supply lines. See Underground electric 
supply lines 

Instrument transformers. See also Transformers 

Grounding of, 151; 51 
Grounding conductor ampacity, 93C3; 19 

Insulated 

Conductor, 161 C; 53 



Definition of, Sec. 2; 5 
Definition of, Sec. 2; 1 

Insulation 

Aerial cable systems, 278; 186 

Definition of, Sec. 2; 1 

Factory tests, 274; 185 

Guy insulators, 279 A; 187 

Level, 273; 185 

Material and marking, 271; 185 

Mechanical strength, 277; 186 

Open-conductor supply lines. See Overhead electric 

supply lines, insulation 
Ratio of fiashover to puncture voltage, 272; 185 
Shielding, definition of, Sec. 2; 1 
Span-wire insulators, 279B; 187 
Special applications, 275; 185 

Insulator 

Definition of, Sec. 2; 7 

Grade of construction, 243C, 2631; 160, 182 

Installing, 447; 240 

Loads upon, 252; 169 

Maintaining, 447; 240 

Span, 279B; 187 

Suspension, 235B2, 235E2; 126, 138 

Intent of National Electrical Safety Code, 015; 2 

Interactive system, utility, definition of, Sec.2; 12 

International System of Units (SI), 017 'A; 3 

Introduction to National Electrical Safety Code, 

Sec. 1; 1 

Inverters, 180E1; 56 

Iron, pulling, definition of, Sec. 2; 9 

Isolated, definition of, Sec. 2; 7 

Isolated by elevation, definition of, Sec. 2; 1 

Isolated-phase bus, 181B; 56 

Isolating switch, definition of, Sec. 2; 5 

Isolation of conductors, 163B; 53 

Isolator. See Disconnecting switch; Isolating switch 



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INDEX 



Jacket, cable, definition of, Sec. 2; 4 

Jacket, definition of, Sec. 2; 7 

Joints, 322; 193 

Joint use, 222; 65 
Definition of, Sec. 2; 7 



Ladders, 420 J; 217 

Lanyards, 441B, 411C; 215 
Definition of, Sec. 2; 1 

Lateral conductor, definition of, Sec. 2; 5 

Lattice structures, 252B2c; 169 

Length, span, definition of, Sec. 2; 1 1 

Lighting. See Illumination 

Lightning circuits, 92B1, 97 A; 16, 25 

Lightning protection equipment, 93D4; 20 

Limited access highway, definition of, Sec. 2; 8 

Line conductor, definition of, Sec. 2; 5 

Lines. See Lines, communication; Lines, electric supply 

Lines, communication 

Definition of, Sec. 2; 8 
Fiber-optic cable, Sec. 2, 230F; 6, 70 
Grounding, 97, 99, 315; 26, 191 
Installation and maintenance 
Overhead. See Overhead communication lines 
Underground. See Underground communication 
lines 
Operation. See Operation of communication systems, 
employee rules; Operation of communication 
systems, employer rules 

Lines, electric supply 

Definition of, Sec. 2; 8 

Fiber-optic cable, Sec. 2, 230F; 6, 70 

Installation and maintenance 
Overhead. See Overhead electric supply lines 
Underground. See Underground electric supply 
lines 



Operation. See Operation of electric supply systems, 
employee rules; Operation of electric supply 
systems, employer rules 

Line supports. See Supporting structures 

Line-worker's body belt, Sec. 2, 420K; 8, 217 
Definition of, Sec. 2; 4 

Liquefied petroleum gas (LPG), 127K; 48 

Liquid-cell batteries, 420G; 217 

Liquid hydrogen systems, 127H; 48 

Liquids, flammable. See Flammable liquids 

Live lines and equipment, work on 

Approach distance, 441 A, 441 B; 224, 232 
Bare-hand method, bonding and shielding for, 446D; 

239 
Capacitors, 4431; 236 
Clear live-line tool length, 441 C; 233 
Connections, making, 443F; 236 
Current transformer secondaries, 443H; 236 
De-energizing to protect employees, 444; 237 

Employee's protective grounds, 444D; 237 

Employee's request, 444B; 237 

Operating switches, disconnectors, and tagging, 
444C; 237 

Proceeding with work, 444E; 238 

Re-energizing, sequence of, 444H; 238 

Reporting clear, 444F1; 238 

Tags, removal of, 444G; 238 

Transferring responsibility, 444F2; 238 
Delta circuits, unintentional grounds on, 443L; 237 
Employee-assisting requirements, 443B; 236 
Equipment, 446B; 239 

Gas-insulated, 443 J; 236 
General requirements, 443A; 235 
Protective grounds, 445; 238 

Installing, 445A; 238 

Removing, 445B; 239 
Switching control procedures, 442, 443C, 443E, 
443G; 233, 236 

Designated person, 442 A; 233 

Operation at stations, 442C; 234 

Oral messages, repeating, 442G; 235 

Re-energizing after work, 442D; 234 

Restoration of service after automatic trip, 442F; 
235 

Specific work, 442B; 234 

Tagging circuits associated with work activities, 
442E; 234 
Training, 446A; 239 
Working position, 44 3D; 236 



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Live parts 

Approach distance to, 441A, 441B; 224, 232 
Clearance from, 232C, 234C, 234D; 72, 99, 107 
Guarding, 124, 234C2; 35, 99 

Load control devices, 180E1; 56 

Loading, line, Sec. 25; 161 
Combined ice and wind loading, 250B, 253, Table 

253-1, Table 253-2; 161, 170, 171, 172 
Components, 25 IB; 168 
Conductors, 251; 168 
Extreme wind loading, 250C, 253, Table 253-1, Table 

253-2, 260B2; 161, 170, 171, 172, 173 
Line supports, 252; 169 
Longitudinal, assumed, 252C; 169 
Simultaneous, application of loads, 252D; 170 
Transverse, assumed, 252B; 269 
Vertical, assumed, 252A; 169 
Maps, Fig 250-1, Fig 250-2; 162, 166 

Loading facilities, flammable and combustible 
liquids, 127D; 47 

Logic devices, 180E1; 56 

Longitudinal loading, assumed, 252C; 169 
Changes in construction grade, 252C1; 169 
Communication conductors on unguyed supports, 

252C7; 170 
Deadends, 252C3; 170 
Longitudinal capability, 252C6; 170 
Poles, jointly used, 252C2; 170 
Stringing loads, 252C5; 170 
Unequal spans, 252C4; 170 

Longitudinal strength requirements, 261A4; 175 

LPG (liquefied petroleum gas), 127K; 48 

Luminaires, 238C, 238D, Table 238-2, 239E2b, 
239G3; 147, 148, 150, 151 



M 



Maintenance. See Installation and maintenance 

Manholes, handholes, and vaults, 323; 194 
Access, 323C, 423A, 443K; 196, 220, 237 
Covers, 323D; 196 

Definition of, Sec. 2; 8 
Definitions of, Sec. 2; 7, 8, 12 
Dimensions, 323B; 196 
Drainage, 323G; 197 
Gratings, definition of, Sec. 2; 8 



Identification, 323J; 197 
Ladder requirements, 323 F; 197 
Mechanical protection, 3231; 197 
Routing, 320A; 192 

Bridges, 320A4; 192 

Highways and streets, 320A3; 192 

Natural hazards, 320A2; 192 

Railroad tracks, 320A5; 192 

Submarine crossings, 320A6; 192 

Tunnels, 320A4, Sec. 39; 192, 212 
Separation from other underground installations, 
320B; 192 

Fuel lines, 320B5; 193 

Sewers, sanitary and storm, 320B3; 193 

Steam lines, 320B6; 193 

Supply conduit systems, 320B2; 193 

Water lines, 320B4; 193 
Strength, 323A; 194 
Testing for gas in, 423B; 220 
Vault and utility tunnel access, 323 E; 196 

Ventilation, 323H; 197 

Manual, definition of, Sec. 2; 8 

Manual stopping devices, 1 3 0B; 49 

Maps, overhead line loading, Fig 250-1, Fig 250-2; 
162, 166 

Mats, 124C4; 35 

Maximum total sag, definition of, Sec. 2; 10 

Measure, units of, 017; 3 

Mechanical protection of conductors, 762, 239D; 53, 
149 

Mechanical transmission machinery, guarding, 

122A; 34 

Messenger wires, grounding, 92C, 93C5, 215C3; 17, 
19,61 

Metal supporting structures, 261A, 261C1; 173, 175 

Methane (natural gas), 127L; 48 

Metric system, 017 A; 3 

Microwave radios, totalizing, 180E1; 56 

Minimum approach distance, definition of, Sec. 2; 8 

Mobile hydrogen systems, 129; 48 



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INDEX 



Motor generators. See Generators 

Motors 

Adjustable-speed, HOE; 49 
Control, 130, 131, 180D; 49, 56 
Short-circuit protection, 133; 49 
Speed limit, 130C; 49 

Movement envelope, conductor, 233 Al, Fig 233-1, Fig 
233-2; 85, 86, 87 

Multigrounded/multiple grounded systems, 96C, 

97D2; 24, 25 
Definition of, Sec. 2; 8 
Multiple-duct conduit, definition of, Sec. 2; 5 

N 

National Electrical Code (NEC), Oil; 1 

National Electrical Safety Code (NESC) 

Application, 013; 1 

Definitions of special terms, Sec. 2; 4 

Effective date, 016; 3 

Intent, 015; 2 

Introduction to, Sec. 1; 1 

Purpose, 010; 1 

Rules, 012; 1 

Scope, Oil; 1 

Units of measure, 01 7; 3 

Waiver, 014; 2 

Natural gas (methane), 127L; 48 

NEC. See National Electrical Code 

NESC. See National Electrical Safety Code 

Neutral conductors, 230E, 242E; 70, 156 
Definition of, Sec. 2; 8 

New equipment, inspection of, 121D; 34 

New installations, 013A; 1 

N grade construction. See Grades of construction 

Nonshielded conductors, 92B2a; 16 

o 

Oil-containing circuit-interrupting devices, 772; 54 



Open conductors, 261 H; 177 

Definition of, Sec. 2; 5 

Operation of communication systems, employee 
rules, Sec. 42, Sec. 43; 216, 222 
General operating routines, 421, 430; 219, 222 

Area protection, 421B; 219 

Duties of first-level supervisor or person in charge, 
421A; 219 

Escort, 421C; 219 
Overhead line operating procedures, 422; 220 

Checking structures before climbing, 422B; 220 

Installing and removing wires or cables, 422C; 220 

Joint-use structures, 432; 222 

Setting, moving, or removing poles in or near 

energized electric supply lines, 422A; 220 
Personal general precautions, 420; 216 

Arcing conditions, 420F; 111 

Cable reels, 420O; 218 

Clothing, 4201; 111 

Energized or unknown conditions, 420D, 431, 
Table 431-1; 216,222,223 

Fall protection, 420K; 211 

Fire extinguishers, 420L; 218 

Fuses, 420N; 218 

Ladders and supports, 420J; 217 

Lighting, street and area, 420P; 219 

Liquid-cell batteries, 420G; 217 

Machines or moving parts, 420M; 218 

Purpose of code, 400; 213 

Qualifications of employees, 420B; 216 

Rules and emergency methods, 420 A; 216 

Safeguarding oneself and others, 420C; 216 

Scope of code, 401; 213 

Tools and protective equipment, 420H; 217 

Ungrounded metal parts, 420E; 216 
Purpose of code, 400; 213 
Scope of code, 401; 213 
Underground line operating procedures, 423; 220 

Excavation, 423D; 221 

Flames, 423C; 221 

Guarding manhole and street openings, 423A, 433; 
220, 222 

Identification, 423E; 221 

Operation of power-driven equipment, 423 F; 221 

Sheath continuity, 434; 222 

Testing for gas in manholes and unventilated vaults, 
423B; 220 

Operation of communication systems, employer 
rules, Sec. 41; 214 
Emergency procedures and first-aid rules, 410B; 214 
General requirements, 420; 214 
Protective methods and devices, 411; 214 
Devices and equipment, 41 IB; 215 
Fall protection, 41 IF; 215 
Identification and location, 41 IE; 215 



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Inspection and testing of protective devices, 41 1C; 
215 

Methods, 411 A; 214 

Warning signs, 411D; 215 
Purpose of code, 400; 213 
Scope of code, 407/213 

Operation of electric supply systems, employee rules, 

Sec. 42, Sec. 44; 216, 224 
Energized lines and equipment. See also Live lines 
and equipment, work on 

Approach distance, 441 A, 441B; 224, 232 

Clear live-line tool length, 441 C; 233 

De-energizing to protect employees, 444; 237 

Work on, 443, 446; 235, 239 
General operating routines, 421, 440; 219, 224 

Area protection, 42 IB; 219 

Duties of first-level supervisor or person in charge, 
421 A; 219 

Escort, 421C; 219 
Overhead line operating procedures, 422; 220 

Checking structures before climbing, 422B; 220 

Installing and removing wires or cables, 422C; 220 

Setting, moving, or removing poles in or near 
energized electric supply lines, 422A; 220 
Personal general precautions, 420; 216 

Arcing conditions, 420F; 111 

Cable reels, 420O; 218 

Clothing, 4201; 211 

Energized or unknown conditions, 420D, 441; 216, 
224 

Fall protection, 420K; 217 

Fire extinguishers, 420L; 218 

Fuses, 420N; 218 

Ladders and supports, 420J; 211 

Lighting, street and area, 420P; 219 

Liquid-cell batteries, 420G; 217 

Machines or moving parts, 420M; 218 

Purpose of code, 400; 213 

Qualifications of employees, 420B; 216 

Rules and emergency methods, 420 A; 216 

Safeguarding oneself and others, 420C; 216 

Scope of code, 401; 213 

Tools and protective equipment, 420H; 217 

Ungrounded metal parts, 420E; 216 
Protective grounds, 445; 238 

Installing, 445A; 238 

Removing, 445B; 239 
Purpose of code, 400; 213 
Scope of code, 401; 213 
Switching control procedures, 442; 233 

Designated person, 442A; 233 

Operation at stations, 442C; 234 

Oral messages, repeating, 442G; 235 

Re-energizing after work, 442D; 234 

Restoration of service after automatic trip, 442F; 
235 



Specific work, 442B; 234 

Tagging circuits associated with work activities, 

442E; 234 
Underground line operating procedures, 423; 220 
Excavation, 423 D; 221 
Flames, 423C; 221 
Guarding manhole and street openings, 423 A, 

443K; 220, 237 
Identification, 423 E; 221 

Operation of power-driven equipment, 423 F; 221 
Testing for gas in manholes and unventilated vaults, 

423B; 220 

Operation of electric supply systems, employer rules, 

Sec. 41; 214 

Emergency procedures and first-aid rules, 410B; 214 

General requirements, 410; 214 

Protective methods and devices, 411; 214 
Devices and equipment, 41 IB; 215 
Fall protection, 411F; 215 
Identification and location, 41 IE; 215 
Inspection and testing of protective devices, 41 1 C; 

215 
Methods, 411A; 214 
Warning signs, 411D; 215 

Purpose of code, 400; 213 

Scope of code, 401; 213 

Outdoor installations, power transformers and 
regulators, 152A; 51 

Out of service, definition of, Sec. 2; 8 

Overhead communication lines 

Accessibility, 213, 216; 60, 62 
Application of rules, 202; 59 
Clearances, Sec. 23; 69 

Antennas, 234, Table 234-1, Table 234-5, 2351; 96, 
101, 121, 141 

Application of code, 230A; 69 

Beaches, 234E2; 109 

Billboards, 234C, Table 234-1; 99, 101 

Bridges, 234, Table 234-1; 96, 101 

Buildings, 234, Fig 234-1, 234C, Table 234-1, 
Table 234-4; 96, 97, 99, 101, 120 

Chimneys, 234C, Table 234-1, Table 234-5; 99, 
101,121 

Climbing space. See Climbing space 

Covered conductors, 230D; 70 

DC circuits, 230G; 70 

Definition of, Sec. 2; 4 

Diagonal, 235D; 133 

Envelope, 233A2, Fig 233-1, Fig 233-3, Fig 234-4; 
85,86,89,115 

Equipment, 234 J; 118 

Fiber-optic cable, 230F; 70 

Grain bins, 234F; 114 



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INDEX 



Ground, 231B, 232, Table 232-1, Table 232-2; 71, 

74,81 
Horizontal, 233B, 234A, Fig 234-1, 234C1, 234D1, 
235B, Table 235-1, Table 235-2, Table 235- 
3; 89, 96, 97, 99, 107, 121, 123, 124, 125 
Measurement, 230B; 69 
Movement envelope, 233A1, Fig 233-1, Fig 233-2; 

85, 86, 87 
Neutral conductors, 230E; 70 
Rail cars, 2341, Fig 234-5; 118, 119 
Roadways, 231B, 232, Table 232-1, Table 232-2; 

71,74,81 
Signs, Table 234-5; 121 
Spacing between, 23 5H; 141 
Supporting structures, 231, 233, 234B, 234 J; 71, 

85,96,118 
Swimming pools, 234, Fig 234-3, Table 234-3; 96, 

109, 113 
Tanks, 234C, Table 234-1, Table 234-5; 99, 101, 

121 
Uniform system of (adopted in 1990 NESC 

edition), Appendix A; 241 
Vertical, 232, 233C, 234, Fig 234-1, 235C, 238; 71, 

89, 96, 97, 126, 147 
Water surfaces. See Water, clearance from 
Wind displacement. See Loading, line 
Working space. See Working space 
Climbing space. See Climbing space 
Communication circuits located within the supply 

space, 224A; 66 
Communication and supply facilities located on same 

structure, 238; 147 
Conductors. See Conductors 
Conflict between lines, avoiding, 221; 65 
Electric railway construction, 225; 67 
Guards under bridges, 225E; 68 
High-voltage contact conductors, 225B; 67 
Prevention of contact loss at railroad crossings at 

grade, 225D; 67 
Third rails, 225C; 67 

Trolley-contact conductor fastenings, 225A, 234A3, 
234D2, 241C3b, 242B, 243, 261H3; 67, 96, 
109, 155, 156, 160, 178 
General requirements, Sec. 21; 60 
Grades of construction. See Grades of construction 
Grounding, 215; 61 
Circuits, 215B; 61 

Guys, 92C, 93C5, 215C2; 17, 19, 61 
Messengers, 92C, 93C5, 215C3; 17, 19, 61 
Supporting structures, 215C1; 61 
Identification, 220D; 65 
Inspection 
When in service, 214A; 60 
When out of service, 214B; 60 
Joint use of structures, 222; 65 
Loading. See Loading, line 
Protective requirements, 223; 66 
Purpose of code, 200; 59 



Relative levels, 220; 64 

Scope of code, 20i; 59 

Span wires, 238C, Table 238-2; 147, 148 

Strength requirements. See Strength requirements 

Supply circuits located within the communication 
space, 224B, 239F, 239G; 67, 150 

Supporting structures. See Supporting structures 

Switches. See Switches 

Tests 
When in service, 214A, 313A; 60, 190 
When out of service, 214B, 313B; 60, 190 

Tree trimming, 218; 63 

Overhead electric supply lines 

Accessibility, 213, 216; 60, 61 
Application of rules, 202; 59 
Clearances, Sec. 23; 69 
Antennas, 234, Table 234-1, Table 234-5, 2351; 96, 

102, 121, 141 
Application of code, 230 A; 69 
Beaches, 234E2; 109 
Billboards, 234C, Table 234-1; 99, 102 
Bridges, 234, Table 234-4; 96, 120 
Buildings, 234, Fig 234-1, 234-C, Table 234-1, 

Table 234-4; 96, 98, 99, 101, 120 
Chimneys, 234C, Table 234-1, Table 234-5; 99, 

101, 121 
Climbing space. See Climbing space 
Covered conductors, 230D; 70 
DC circuits, 230G; 70 
Definition of, Sec. 2; 4 
Diagonal, 235D; 133 

Envelope, 233A2, Fig 233-1, Fig 233-3; 85, 86, 89 
Equipment, 234 J; 118 
Fiber-optic cable, 230F; 70 
Grain bins, 234F; 114 
Horizontal, 233B, 234A, Fig 234-1, 234C1, 234D1, 

235B, Table 235-1, Table 235-2, Table 235- 

3; 89, 96, 98, 99, 107, 121, 123, 124, 125 
Measurement, 230B; 69 
Movement envelope, 233A1, Fig 233-1, Fig 233-2; 

85, 86, 87 
Neutral conductors, 230E; 70 
Rail cars, 2341, Fig 234-5; 118, 119 
Roadways, 231B, 232, Table 232-1, Table 232-2; 

71,74,81 
Signs, Table 234-5; 121 
Supply cables, 230C; 69 
Supporting structures, 231, 233, 234B, 234 J; 71, 

85,96,118 
Swimming pools, 234, Fig 234-3, Table 234-3; 96, 

109, 113 
Tanks, 234C, Table 234-1, Table 234-5; 99, 102, 

121 
Uniform system of (adopted in 1990 NESC 

edition), Appendix A; 241 
Vertical, 232, 233C, 234, Fig 234-1, 235C, 238; 71, 

89, 96, 98, 126, 147 



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Water surfaces. See Water, clearance from 

Wind displacement. See Loading, line 
Climbing space. See Climbing space 
Communication and supply facilities located on same 

structure, 238; 147 
Communication circuits located within the supply 

space, 224A; 66 
Conductors. See Conductors 
Conflict between lines, avoiding, 227; 65 
Electric railway construction, 225; 67 

Guards under bridges, 225E; 68 

High- voltage contact conductors, 225B; 67 

Prevention of contact loss at railroad crossings at 
grade, 225D; 67 

Third rails, 225C; 67 

Trolley-contact conductor fastenings, 225 A, 234A3, 
234D2, 241 C3b, 242B, 243, 261H3; 67, 96, 
109, 155, 156, 160, 178 
General requirements, Sec. 21; 60 
Grades of construction. See Grades of construction 
Grounding, 215B; 61 

Circuits, 215B; 61 

Guys, 92C, 93C5, 215C2; 17, 19, 61 

Messengers, 92C, 93C5, 215C3; 17, 19, 61 

Supporting structures, 215C1; 61 
Identification, 220D; 65 
Inspection 

When in service, 214A; 60 

When out of service, 214B; 60 
Insulation, Sec. 27; 185 

Aerial cable systems, 278; 186 

Definition of, Sec. 2; 7 

Factory tests, 274; 185 

Guy insulators, 279A; 187 

Level, 273; 185 

Material and marking, 277; 185 

Mechanical strength, 277; 186 

Open-conductor supply line. See Overhead electric 
supply lines, insulation 

Ratio of flashover to puncture voltage, 272; 185 

Shielding, definition of, Sec. 2; 7 

Span-wire insulators, 279B; 187 

Special applications, 275; 169 
Joint use of structures, 222; 65 
Loading. See Loading, line 
Purpose of code, 200; 59 
Relative levels, 220; 64 
Scope of code, 207; 59 

Strength requirements. See Strength requirements 
Supply circuits located within the communication 

space, 224B, 239F, 239G; 67, 150 
Supporting structures. See Supporting structures 
Switches. See Switches 
Tests 

When in service, 2744, 313A; 60, 190 

When out of service, 214B, 313B; 60, 190 
Tree trimming, 218; 63 



Overhead shield wires, 26777; 177 

Overspeed trip device for prime movers, automatic, 

130A; 49 



Pad-mounted equipment, definition of, Sec. 2; 8 
Part, current-carrying, definition of, Sec. 2; 5 
Passageways, supply station, 112B; 32 
Person, designated, definition of, Sec. 2; 5 
Pins (line support), 234C, 252, 261F; 160, 169, 177 

Piping systems as grounding electrodes, 94A, 95B; 

21,24 

Plates, buried, as grounding electrodes, 94B3c; 22 
Plowing, 352B; 204 

Poles 

See also Supporting structures 

Butt plates as grounding electrodes, 94B4; 22 

Loads on, 252; 169 

Strength requirements, Sec. 26; 173 

Positioning device system, definition of, Sec. 2; 9 

Positioning straps, 411B, 420K; 215, 217 
Definition of, Sec. 2; 9 

Power transformers, 752; 51. See also Transformers 
Indoor installations, 7526; 51 
Outdoor installations, 752A; 51 
Short-circuit protection, 755; 51 

Precipitator logic devices, 180E1; 56 

Pressure, side-wall, definition of, Sec. 2; 1 1 

Prestressed-concrete structures, 267 Al, Table 261-1, 
261C1; 173, 175, 180 
Definition of, Sec. 2; 9 

Protective grounding. See Grounding 

Protective methods and devices. See Operation of 
electric supply systems, employee rules; 
Operation of electric supply systems, employer 
rules 



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INDEX 



Pulling iron, definition of, Sec. 2; 9 
Pulling tension, definition of, Sec. 2; 9 
Puncture voltage, insulation, 272; 185 
Purpose of National Electrical Safety Code, 010; 1 

Q 

Qualified, definition of, Sec. 2; 9 
Qualified climber, Sec. 2, 420K2; 9, 201 

R 

Raceway 

Definition of, Sec. 2; 9 

Grounding conductors for, 93C5; 19 

Racks, battery, 143; 50 

Radios, microwave, totalizing, 180E1; 56 

Railings, 112, Fig 124-2; 32, 44 

Railroads. See also Electric railway construction 
Ballast section, definition of, Sec. 2; 4 
Clearances, 23 1C, 232, 234; 71, 96 

Underground, 320A5, 351C3; 192,203 
Grades of construction, 241C3b, 242B, 243; 155, 156, 
160 

Random separation 

Definition of, Sec. 2; 9 
Direct buried cable, 354; 205 

Readily climbable supporting structure, Sec. 2, 
217A2; 9, 62 

Reclosers, Sec. 17; 54 
Application, 171; 54 
Arrangement, 770; 54 
Capacity, 173 A; 54 
Oil-containing, 172; 54 
Provisions for disconnecting, 17 3B; 54 
Visible break switch, 173C; 54 

Re-energizing after work, 442 D, 444H; 234, 238 

Regulators 

Indoor installations, 152B; 51 
Outdoor installations, 152 A; 51 



Reinforced concrete structures, Table 253-2, 261 Al, 
261C2, Table 261-1; 111, 173, 175, 180 

Reinforcing bars as grounding electrodes, 94 A3, 

95A3; 21, 23 

Relay logic devices, 180E1; 56 

Remotely operable (as applied to equipment), 
definition of, Sec. 2; 9 

Resistance requirements, grounding systems, 96; 24 

Multi-grounded systems, 96C; 24 
Single-grounded systems, 96B; 24 
Supply stations, 96 A; 24 

Ridge-pin conductors, 2361; 144 

Risers, Sec. 36; 208 
Installation, 361; 208 
Pad-mounted installations, 363; 208 
Pole risers, 362; 208 

Roadways 

Clearances from 

Overhead, 231B, 232, Table 232-1, Table 232-2; 71, 
74,81 

Underground, 320A3, 351C4; 192, 204 
Definition of, Sec. 2; 9 
Shoulder, definition of, Sec. 2; 1 1 
Traveled way, definition of, Sec. 2; 12 

Rods as grounding electrodes, 94B2; 22 

Rotating equipment, Sec. 13; 49 
Motor control, 131; 49 
Short-circuit protection, 133; 49 
Speed control and stopping devices, 130; 49 

Rules, National Electrical Safety Code, 012; 1 

Rural districts, definition of, Sec. 2; 9 

s 

Safety, employee. See Operation of electric supply 
systems, employee rules 

Safety, employer. See Operation of electric supply 
systems, employer rules 

Safety clearance zone, electric supply stations, 

110A2, Fig 110-1; 28, 29 



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Safety zone, communication worker, 235C4, 238E; 
133, 147 

Sag 

Apparent, at any point in a span (definition), Sec. 2; 

10 
Apparent, of a span (definition), Sec. 2; 10 
Clearance considerations 
Conductors of different sag on same support, 

235C2b; 127 
Horizontal clearance, 235Blb, Table 235-2, 
Table 235-3; 122, 124, 125 
Conductor, definition of, Sec. 2; 10 
Definition of, Sec. 2; 9 
Final, definition of, Sec. 2; 10 
Final unloaded, definition of, Sec. 2; 10 
Initial unloaded, definition of, Sec. 2; 9 
Total, definition of, Sec. 2; 10 

Scope of National Electrical Safety Code, 011; 1 

Separation, definition of, Sec. 2; 10 

Separation, random 

Definition of, Sec. 2; 9 
Direct buried cable, 354; 205 

Separation of grounding conductors, 97; 25 

Service. See In service; Out of service 

Service drop, definition of, Sec. 2; 10 

Service point, definition of, Sec. 2; 10 

Settings, strength of, 261 B; 175 

Sewers, separation from underground lines, 320B3, 
354E; 193, 207 

Sheath, cable, definition of, Sec. 2; 4 

Sheath transposition connections (cross-bonding), 

93E6; 21 

Shielded conductors, 92B2b; 16 
Shielding, conductor, definition of, Sec. 2; 5 
Shielding, insulation, definition of, Sec. 2; 7 
Shields, 124C2; 35 
Shield wire/conductor, definition of, Sec. 2; 10 



Short-circuit protection 

Motors, 133; 49 

Power transformers, 153; 51 

Short-time ampacity, grounding conductor, 93 C; 19 

Shoulder, definition of, Sec. 2; 1 1 

SI (International System of Units), 17 A; 3 

Side-wall pressure, definition of, Sec. 2; 1 1 

Signs, 217A4, Table 234-5, 41 ID; 63, 121, 215 

Single-duct conduit, definition of, Sec. 2; 5 

Single-grounded system, definition of, Sec. 2; 1 1 

Snaphooks, positioning strap, 420K; 217 

Solid-state logic devices, 180E1; 56 

Soot blower control devices, 180E1; 56 

Spacer cable, definition of, Sec. 2; 1 1 

Span 

Length, definition of, Sec. 2; 1 1 
Sag, definitions of, Sec. 2; 10 
Wire 

Clearances from communication lines, 238C, Table 
238-2; 147, 148 

Definition of, Sec. 2; 1 1 

Insulators, 279B; 187 

Speed control and stopping devices, 130; 49 
Adjustable-speed motors, 130E; 49 
Automatic overspeed trip device for prime movers, 

130A; 49 
Manual stopping devices, 130B; 49 
Protection of control circuits, 130F; 49 
Speed limit for motors, 130C; 49 

Stairs and steps 

Supply stations, 112; 32 

Supporting structures, 217A2, 239B; 62, 149 

Standoff brackets, 217 A2c, 239J; 63, 152 

Static wire, definition of, Sec. 2; 10 

Station, electric supply, definition of, Sec. 2; 6 

Station, generating, definition of, Sec. 2; 6 



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Steam lines, separation from underground conduit, 

320B6; 193 

Steel Wire Gage (Stl WG), Sec. 2; 13 

Steps. See Stairs and steps 

Stopping devices. See Speed control and stopping 
devices 

Storage batteries, Sec. 14; 50 
Employee precautions, 420G; 217 
Floors in battery areas, 144; 50 
Illumination for battery areas, 745; 50 
Location, 141; 50 
Racks, 143; 50 
Service facilities, 146; 50 
Ventilation, 142; 50 

Strap (positioning), 41 IB, 420K; 215, 217 
Definition of, Sec. 2; 9 

Streets, clearances from, 23 IB; 71 

Underground, 320A3, 351C4; 192, 204 

Strength requirements, Sec. 26; 173 
Grades B and C construction, 261; 173 

Armless, 261 G; 177 

Braces, 261D; 176 

Communication cables, 261K; 178 

Communication conductors, open-wire, 261J; 178 

Communication conductors, paired, 261 L; 178 

Crossarms, 261D; 176 

Fastenings, 261F; 177 

Foundations, 261 B; 175 

Guy anchors, 261B; 175 

Guys and guy insulators, 261 C; 175 

Open supply conductors, 261H; 177 

Overhead shield wires, 261H; 177 

Pins, 261F; 111 

Settings, 261B; 175 

Supply cable messengers, 2611; 178 

Support hardware, 261M; 179 

Supporting structures, 261 A; 173 
Grade N construction, 263; 181 

Communication conductors, 263G; 182 

Crossarm strength, 263C; 181 

Guys, 263B; 181 

Insulators, 2631; 182 

Poles, 263 A; 181 

Service drops, 263E, Table 263-2; 181, 183 

Street and area lighting equipment, 263H; 182 

Supply-line conductors, 263D, Table 263-1; 181, 
182 

Trolley-contact conductors, 263 F; 182 
Guying and bracing, 264; 183 



Anchor rods, 264G; 184 
Electrolysis, 264F; 184 
Fastenings, 264D; 183 
Markers and Protection, 264E; 184 
Point of attachment, 264C; 183 
Strength, 264B; 183 
Where used, 264 A; 183 

Strips, buried, as grounding electrodes, 94B3b; 22 

Structure conflict, definition of, Sec. 2; 1 1 

Structures, supporting. See Supporting structures 

Submarine crossings, 320A6, 351C5; 192, 204 

Substation, definition of, Sec. 2; 6 

Suddenly moving parts, guarding, 122B; 34 

Sulfur dust, 1271; 48 

Supply equipment, electric, definition of, Sec. 2; 6 

Supply lines, electric. See Lines, electric supply 

Supply stations, electric 

Definition of, Sec. 2; 6 
Generating station, definition of, Sec. 2; 6 
Ground resistance requirements, 96A; 24 
Protective arrangements, Sec. 11; 28 

Electric equipment, HOC; 30 

Enclosures, 110A; 28 

Exits, 113; 33 

Fire-extinguishing equipment, 114; 33 

Floors, 112A; 32 

Illumination, 111; 30 

Passageways, 112B; 32 

Railings, 112C; 33 

Rooms and spaces, HOB; 28 

Stair guards, 112D; 33 

Top rails, 112E; 33 
Purpose of code, 100; 27 
Scope of code, 101; 21 
Substation, definition of, Sec. 2; 6 

Support arms, 232B, 243B; 72, 160 

Support hardware, 253, 261 M; 170, 179 

Supporting structures 

Armless construction brackets, 243 C; 160 
Clearances from other objects, 231; 71 

Fire hydrants, 231 A; 11 

Railroad tracks, 231C; 71 



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INDEX 



Streets, roads, highways, 23 IB; 71 
Climbing. See Climbing space 
Conductor fastenings, 243C, 252, 26 IF; 160, 169, 

177 
Crossarms, 243B, 253, Table 253-1; 160, 170, 171 
Decorative lighting, 21 7A5; 63 
Definition of, Sec. 2; 1 1 
Different, clearances between conductors carried on, 

233, Table 233-1; 85, 91 
Grades of construction, 243 A; 160 
Grounding of, 215C1; 61 
Identification, 217 A3, 220E; 63, 65 
Insulators, 243C; 160 
Loads upon, 252; 169 

Longitudinal, assumed, 252C; 169 

Simultaneous application of, 252D; 170 

Transverse, assumed, 252B; 169 

Vertical, assumed, 252A; 169 
Metal, 261A, 261C1, Table 261-1; 173, 175, 180 
Obstructions, 217A4; 63 
Pins, 243C; 160 
Prestressed concrete, Sec. 2, 261 Al, 261C1, Table 

261-1; 9, 173, 175, 180 
Protection of, 217 Al; 62 
Readily climbable, Sec. 2, 217A2; 9, 62 
Reinforced concrete, Table 253-2, 261A1, 261C2, 

Table 261-1; 172, 173, 175, 180 
Standoff brackets, 217 A2c; 63 
Steps, 217A2; 62 

Strength requirements. See Strength requirements 
Support arms, 243B; 160 
Support hardware, 253, 261M; 170, 179 
Unusual, 217B; 63 

Wood, 261A2, 261C2, Table 261-2; 174, 175, 181 
Working space. See Working space 

Surge arresters, Sec. 19; 58 
Grounding conductors, 192; 58 

Ampacity, 93C4; 19 
Indoor locations, 191; 58 
Installation, 193; 58 

Susceptiveness, definition of, Sec. 2; 1 1 

Suspension insulators, 235B2, 235E2; 126, 138 

Swimming pools, 234, Fig 234-3, Table 234-3, 351 CI; 
96,109,113,203 

Switchboards 

Control, 180E; 56 
Dead-front, 180C; 56 
Definition of, Sec. 2; 1 1 

Switches 

Application, 171; 54 



Arrangement, 170, 216; 54, 62 
Capacity, 173 A; 54 
Definition of, Sec. 2; 1 1 
Disconnecting, Sec. 17; 54 

Definition of, Sec. 2; 5 
Isolating, definition of, Sec. 2; 5 
Oil-containing, 172; 54 
Protecting employees by, 443E; 236 
Visible-break, 173C; 54 

Switchgear assemblies 

Control switchboards, 180E; 56 
Dead-front power switchboards, 180D; 56 
De-energizing, 443G; 236 
General requirements, 180A; 55 
Metal-enclosed power switchgear, 180B; 55 
Motor control centers, 180D; 56 

System, conduit, definition of, Sec. 2; 5 

System, grounded, definition of, Sec. 2; 1 

Systeme International d'Units (SI), 017 A; 3 

T 

Tag, definition of, Sec. 2; 1 1 

Tanks, conductor clearance from, 234C, Table 234-1, 
Table 234-5; 99, 102, 121 

Telemetering devices, 180E1; 56 

Temporary overhead installations, 014B; 2 

Tension, pulling, definition of, Sec. 2; 9 

Tension, unloaded 

Final, definition of, Sec. 2; 12 
Initial, definition of, Sec. 2; 12 

Terminal, cable, definition of, Sec. 2; 4 

Terminations, conductor, 164; 53 

Terminations, underground supply cable, Sec. 37; 
209 
Clearances in enclosures or vaults, 373; 209 
Grounding, 374; 209 
Identification, 372; 209 
Support, 371; 209 

Terms, definitions of, Sec. 2; 4 



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INDEX 



Tests 

For gas in manholes and unventilated vaults, 423B; 
220 

Insulation, 274; 185 

Lines and equipment 
When in service, 214A, 313A; 60, 190 
When out of service, 214B, 313B; 60, 190 

Protective devices, 41 1 C; 215 

Third rails, 225C; 67 

Totalizing microwave radios, 180E1; 56 

Total sag, definition of, Sec. 2; 10 

Total sag, maximum, definition of, Sec. 2; 10 

Towers. See Supporting structures 

Traffic signals, 238, Table 238-2, 239G; 147, 148, 150 

Training, 446A; 239 

Transferring (fall protection), definition of, Sec. 2; 1 1 

Transformers, Sec. 15; 5 1 
Current-transformer secondary circuits protection 

when exceeding 600 V, 150; 51 
Grounding secondary circuits of instrument 

transformers, 151; 51 
Instrument, 93C3, 151; 19, 51 
Location and arrangement of power transformers and 
regulators, 152; 51 
Indoor installations, 152B; 51 
Outdoor installations, 152A; 5 1 
Short-circuit protection, 153; 51 

Transformer vault, definition of, Sec. 2; 1 1 

Transitioning (fall protection), definition of, Sec. 2; 
11 

Transverse loading, assumed, 252B; 169 
At angles, 252B3; 169 
Conductors, 252B1; 169 
Messengers, 252B1; 169 
Span lengths, 252B4; 169 
Structure, 252B2, 261 A3; 169, 175 

Traveled way, definition of, Sec. 2; 12 

Tree trimming, 218; 63 

Trenching, 352A; 204 



Trolley-contact conductors, 225A, Table 233-1, 

234A3, 234D2, 238C, 239G, 241C3b, 242B, 243, 
261H3; 64, 91, 96, 109, 147, 150, 155, 156, 160, 

178 

Tunnels, 320A4, Sec. 39; 192, 212 

u 

Underground communication lines, Part 3; 189 
Accessibility, 312; 190 
Application of rules, 302; 189 
Direct buried cable, Sec. 35; 202 

Deliberate separation, 353; 205 

Installation, 352; 204 

Random separation, 354; 205 

Routing, 351; 202 

Symbols for identification of, Fig 350-1; 203 
Equipment, Sec. 39; 210 

Design, 381; 210 

Grounding, 384; 211 

Identification, 385; 211 

Installation, 383; 111 

Location in underground structures, 382; 211 
General requirements, Sec. 31; 190 
Grounding, 314; 190 

Circuits, 314C; 191 

Conductive parts to be grounded, 314B; 190 

Methods, 314A; 190 
Induced voltage, 316; 191 
Inspection 

When in service, 313A; 190 

When out of service, 313B; 190 
Installation, 311; 190 
Maintenance, 311; 190 
Operating procedures, 423; 220 
Protective requirements, 315; 191 
Purpose of code, 300; 189 
Risers, Sec. 36; 208 

Installation, 361; 208 

Pad-mounted, 363; 208 

Pole, 362; 208 
Scope of code, 301; 189 
Supply cable 

Cable accessories and joints, 333; 198 

Sheaths and jackets, 331; 198 

Shielding, 332; 198 

Terminations, Sec. 37; 209 
Tunnels, installation in, Sec. 39; 212 

Environment, 391; 212 
Underground structures, cable in, Sec. 34; 199 

Bonding, 342; 200 

Communication cables containing special supply 
circuits, 344; 200 

Fireproofing, 343; 200 

Grounding, 342; 200 

Installation, 341; 199 
In manholes and vaults, 341B; 199 



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INDEX 



Underground electric supply lines, Part 3; 189 
Accessibility, 312; 190 
Application of rules, 302; 189 
Direct buried cable, Sec. 35; 202 

Deliberate separation, 353; 205 

Installation, 352; 204 

Random separation, 354; 205 

Routing, 351; 202 

Symbols for identification of, Fig 350-1; 203 
Equipment, Sec. 38; 210 

Design, 381; 210 

Grounding, 384; 211 

Identification, 385; 111 

Installation, 383; 211 

Location in underground structures, 382; 211 
General requirements, Sec. 31; 190 
Grounding, 314; 190 

Circuits, 314C; 190 

Conductive parts to be grounded, 314B; 190 

Methods, 314A; 190 
Induced voltage, 316; 191 
Inspection 

When in service, 3 13 A; 190 

When out of service, 313B; 190 
Installation, 311; 190 
Maintenance, 311; 190 
Operating procedures, 423; 220 
Purpose of code, 300; 189 
Risers, Sec. 36; 208 

Installation, 361; 208 

Pad-mounted, 365; 208 

Pole, 362; 208 
Scope of code, 301; 189 
Supply cable 

Cable accessories and joints, 333; 198 

Sheaths and jackets, 331; 198 

Shielding, 332; 198 

Terminations, Sec. 37; 209 
Tunnels, installation in, Sec. 39; 212 

Environment, 3Pi; 212 
Underground structures, cable in, Sec. 34; 199 

Bonding, 342; 200 

Communication cables containing special supply 
circuits, 344; 200 

Fireproofing, 343; 200 

Grounding, 342; 200 

Installation, 341; 199 
in manholes and vaults, 341B; 199 

Underground grounding conductors, 93E; 20 

Ungrounded circuits, voltage of (definitions), Sec. 2; 
13 

Ungrounded system, definition of, Sec. 2; 12 

Uniform system of clearances (adopted in 1990 NESC 
edition), Appendix A; 241 



Unigrounded system, definition of, Sec. 2; 1 1 
Units of measure, 017; 3 

Unloaded sag 

Final, definition of, Sec. 2; 10 
Initial, definition of, Sec. 2; 9 

Unloaded tension 

Final, definition of, Sec. 2; 12 
Initial, definition of, Sec. 2; 12 

Unloading facilities, flammable and combustible 
liquids, 127D; 47 

Urban districts, definition of, Sec. 2; 12 

Use, common, definition of, Sec. 2; 4 

Utility, definition of, Sec. 2; 12 

Utility interactive system, definition of, Sec. 2; 12 

Utilization equipment, definition of, Sec. 2; 12 

V 
Vaults. See Manholes, handholes, and vaults 
Ventilation, battery area, 142; 50 

Vertical clearance, 232, 233C, 234, 235C, 238; 71, 89, 
96, 126, 147 
From live parts, Fig 124-1, Table 124-1; 36, 37 

Vertical loading component, 251B1, 252A; 168, 169 

Vertical racks, 23 5G; 140 

Visible break switches, 173C; 54 

Voltage 

Of circuit not effectively grounded, definition of, Sec. 

2; 12 
Of constant-current circuit, definition of, Sec. 2; 12 
Definition of, Sec. 2; 12 
Of effectively grounded circuit, definition of, Sec. 2; 

12 
To ground of conductor of grounded circuit, definition 

of, Sec. 2; 13 
To ground of conductor of ungrounded circuit, 

definition of, Sec. 2; 13 
To ground of grounded circuit, definition of, 

Sec. 2; 13 



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INDEX 



To ground of ungrounded circuit, definition of, 
Sec. 2; 13 

w 

Waiver of National Electrical Safety Code rules, 

014; 2 

Water, clearance from, 232, Table 232-1, Table 232-2; 
71,74,81 
Beaches, 234E2; 109 

Swimming pools, 234, Fig 234-3, Table 234-3, 
351C1; 96, 109, 113,203 
Water lines, separation from underground lines, 
320B4, 354E; 193, 207 

Water piping systems as grounding electrodes, 94 A, 

95 B; 21,24 

Way, traveled, definition of, Sec. 2; 12 

Weather loading. See Loading, line 

Wind. See Loading, line 

Wire, buried, as grounding electrode, 94B3a; 22 

Wire, span, definition of, Sec. 2; 1 1 

Wire gages, definition of, Sec. 2; 13 

Wire wraps as grounding electrodes, 94B4; 22 

Wood structures, Table 253-2, 261A2, Table 261-1, 
Table 261-2; 172, 174, 180, 181 

Wording of NESC rules, 075; 2 

Working space 

Buckarms, location relative to, 237D, Fig 237-1; 146 
Dimensions, 237 B; 145 
Energized equipment 

Guarding of, 237E; 146 

Working clearances from, 237F; 146 
Equipment over 600 V, 125B, 45 
Equipment 600 V or less, 125A; 45 
Location, 237 A; 145 

Vertical and lateral conductors, location relative to, 
237C, 239B; 146, 149 

Work rules. See Operation of electric supply systems, 
employee rules; Operation of electric supply 
systems, employer rules 

Worksite (fall protection), definition of, Sec. 2; 13 



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THIS PAGE IS INTENTIONALLY BLANK 



278 
Copyright © 2001 IEEE. All rights reserved. 



REVISION PROCEDURE 



Procedure for Revising the National Electrical Safety Code 



1 . Preparation of Proposals for Amendment 

NOTE: The procedures for the collection of Change Proposals are subject to change as the revision of 
the 2007 Edition of the NESC approaches. Logon to the NESC Zone at http://standards.ieee.org/nesc/ 
for updates. 

1.1 A proposal may be prepared by any 

• Substantially interested person 

• Interested organization 

• NESC Subcommittee 

• Member of the NESC Committee or its subcommittees 

1 .2 Proposals shall be submitted to: Secretary, National Electrical Safety Code Committee (at the ad- 
dress listed on the following Change Proposal Form on p. 261). Copies must be suitable for repro- 
duction and shall be on the forms for new proposals available on p. 261. A diskette containing the 
change proposal text in any electronic form should be submitted in addition to the hard copy. 

1.3 Each separate topic shall begin on a separate form, printed or typed on one side only. If a proposal 
references documents not readily available to all subcommittee members, sufficient copies of the 
referenced documents to supply the subcommittee must be furnished. 

1 .4 The proposal shall consist of 

a. a statement, in NESC rule form, of the exact change, rewording, or new material proposed. 
Words to be deleted shall be stricken through and words to be added shall be underlined. (See 
example on p. 260.) 

b. the name of the submitter (organization or individual as applicable). 

c. supporting comment, giving the reasons why the NESC should be so revised. 

2. The NESC Secretary will 

(a) Acknowledge receipt of proposals for revision. (If the submitter does not receive an acknowledg- 
ment within 30 days of mailing his or her proposal, the Secretary should be contacted.) 

(b) Distribute to each member of the appropriate NESC Subcommittee all of the proposals received, ar- 
ranged in a coordinated sequence. 

3. Subcommittee Recommendation 

The NESC Subcommittee responsible will consider each proposal and take one or more of the following 
steps: 

(a) Endorse the proposal as received. 

(b) Prepare a proposed revision or addition for the NESC (this may be a coordination of several com- 
ments, or a committee consensus on a modification of a proposal). 

(c) Refer the proposal to a technical working group for detailed consideration. 

(d) Request coordination with other NESC Subcommittees. 

(e) Recommend rejection of the proposal, for stated reasons. 

For each item, the responsible subcommittee shall prepare a voting statement, accompanied by all 
members' statements concerning their votes (cogent reasons are required for negative votes). Steps (c) 
and (d) are intended to result, eventually, in a proposal of category (b). 

Action under steps (c) or (d) shall be completed and reported to the subcommittee before the end of 
the public review period if the item is to be included in the upcoming revision. 

4. Preprint of Proposals 

The NESC Secretary shall organize and publish a preprint of the proposed revisions including 
(a) The original proposal as received from the submitter. 



I 



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REVISION PROCEDURE 



(b) The recommendation of the subcommittee with respect to the proposal (including a voting statement 

and subcommittee members' statements). 

(c) Copies of submittal form for comments. 

The preprint shall be distributed to all members of NESC Subcommittees and representatives of or- 
ganizations comprising the NESC Committee. Copies shall be available for sale to other interested par- 
ties. Notice of availability of the preprint shall be submitted to ANSI for publication in ANSI Standards 
Action. The preprint shall carry information on how to submit comments on the proposals and the final 
date for such submissions. 

5. Final Processing of Proposed Revisions and Comments 

5 . 1 Following the public review period, the Secretary shall organize and distribute for subcommittee con- 
sideration all comments received. 

5.2 The preprint and the comments received shall be reconsidered by the subcommittees. No new change 
proposals may be considered. 

(a) The subcommittee may recommend adoption or rejection of the proposal by majority vote. 

(b) When extended technical consideration or resolution of differing or conflicting points of view is 
necessary, the subcommittee shall refer the problem to a working group of the subcommittee for 
proposed resolution. If expeditious resolution is not possible, the subject shall be held on the 
docket. 

Each working group shall provide, to its parent subcommittee, recommendations on matters 
considered as a result of subcommittee referrals under items 3(c) and 5.2(b). 

Each subcommittee shall prepare a report showing its proposed revisions and all items held 
on the docket together with a plan for their disposition. 

5.3 The Secretary shall provide commentors with copies of actions taken on the rules affected by their 
comments, and shall make all such reports available for examination upon request. 

6. Final Approval 

6. 1 Based upon the subcommittee reports, the Secretary shall prepare a draft of the revision of the NESC 
and distribute copies to 

(a) The NESC Committee for approval by a six-week letter ballot. 

(b) The American National Standards Institute Board of Standards Review for concurrent 60-day 
public review. 

6.2 Comments received in response to the letter ballot and public review shall be referred to the Execu- 
tive Subcommittee for resolution or referral to the appropriate subcommittee. Those items on which 
consensus cannot be reached shall be referred to the appropriate subcommittee for consideration dur- 
ing the next revision cycle. Unless a consensus for revision is established, the requirements of the 
current edition shall carry over to the proposed edition. 



Request for Change 
National Electrical Safety Code 




Rule 233Alb(5), revise to read: 

(5) Where crossing is not 
conditiens-whefe-the^ipper- ' 
the additional 
233A1 



id-under 

■3), 
AlbQ) and 



Suppoi 
intent 
which 
ture 



posal for Rule 233Alb(4)] 



determined by- Rules 

that the suggested revision clarifies the 

[y, the revision properly addresses Rule 233Alb(4), 

r conductors designed to operate at a conductor tempera- 

F (50 °C), regardless of span length (based on companion pro- 



280 
Copyright © 2001 IEEE. All rights reserved. 



REVISION PROCEDURE 

FORM FOR CHANGE PROPOSALS ON THE 
NATIONAL ELECTRICAL SAFETY CODE 

(A separate form must be used for each Change Proposal) 
Name Date 



Address 



Organization Represented_ 
1. Rule: 



2. Proposal: Include proposed exact wording, or identification of wording to be deleted. (Underline 
added words, strike through deleted words) 



3. Statement of Problem and Supporting Comments 



Signature . 



Mail to: Secretary-NESC Committee, IEEE Standards Department 
445 Hoes Lane, P.O. Box 1331, Piscataway, NJ 08855-1331 

This form may be duplicated. A diskette containing the change proposal text in any 
electronic form should be submitted, in addition to the hard copy. 



281 
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I 



REVISION PROCEDURE 



Time Schedule for the Next Revision of the 
National Electrical Safety Code 



17 July 2003 



5-24 October 2003 
1 September 2004 
1 May 2005 

2-20 October 2005 

15 January 2006 

15 May 2006 
1 August 2006 



Final date for receipt of proposals from the public for revision of the 
2002 Edition of the National Electrical Safety Code, preparatory to the 
publication of a 2007 Edition. Proposals should be forwarded in the pre- 
scribed form to: 

Secretary 

National Electrical Safety Code 

IEEE Standards Department 

445 Hoes Lane 

P.O. Box 1331 

Piscataway, NJ 08855-1331 

NESC Subcommittees consider proposals for changes to the NESC and 
prepare their recommendations. 

Preprint of Proposed Amendments for incorporation into the 2007 Edi- 
tion of the NESC published for distribution to the NESC Committee and 
other interested parties. 

Period for study of proposed amendments and submittal by interested 
parties of recommendations concerning the proposed amendments. Sub- 
mit recommendations to the Secretary, NESC Committee, at the above 
address. 

Period for NESC Subcommittee Working Groups and NESC Subcom- 
mittees to reconsider all recommendations concerning the proposed 
amendments and prepare final report. 

Proposed revision of the NESC, Accredited Standards Committee C2, 
submitted to NESC Committee for letter ballot and to the American 
National Standards Institute for concurrent public review. 

NESC Committee approved revisions of the NESC submitted to the 
American National Standards Institute for recognition as an ANSI 
standard. 

Publication of the 2007 Edition of the National Electrical Safety Code. 



282 
Copyright © 2001 IEEE. All rights reserved. 



WORKING GROUP ASSIGNMENTS 



Working Group Assignments 

In response to comments received on the NESC Preprint 2002 Proposals, and proposals for change to the 
1997 edition of the Code, members of the technical subcommittees recommended new assignments for exist- 
ing or new working groups. All of these recommendations and subsequent actions are summarized below. 

These working groups are preparing recommendations for the next edition of the NESC. NESC Subcommit- 
tee membership is not required for working group participation. For more information or to participate on any 
working group(s), please contact the NESC Secretary. 

Subcommittee 1, Coordination (SCI) 

Working Group 1.10, Definition and Use of Grounding Terms. A Working Group (WG) of 
Subcommittee 1 was formed to clarify what is meant by the terms "grounded," "effectively grounded," etc., 
as relating to neutral conductors. See CP 2182 on page 63 of the NESC Preprint 2002 Proposals. 
Chair: Allen L. Clapp 

Subcommittee 2, Grounding Methods (SC2) 

Working Group 2.2, Steel Poles as Made Electrodes. A WG was formed to investigate the feasibility of 
accepting steel poles as a man-made electrode in response to CP 2284, Comment 3247 (Rule 94B). 
Chair: John Dagenhart 

Subcommittee 3, Electric Supply Stations (SC3) 

None. 

Subcommittee 4, Clearances-Overhead Lines (SC4) 

Working Group 4.8, Aerial Facilities Clearances. Subject existing aerial clearance rules between commu- 
nications and supply facilities to a comprehensive review that will mirror the significant changes in business 
and technology over the past 1/2 century, with the objective of relieving pole space congestion. The WG will 
concentrate on definitions and Sections 21, 22, and 23, but no work will be done on clearances over terrain 
or from structures. Section 9, Grounding, will be addressed only if required by changes made elsewhere. 
Parts 1,3, and 4 will not be examined. During the proposal portion of the 2002 Code cycle, SC4 voted to ex- 
tend the scope of the WG to include the responsibility of evaluating all new communication technology for 
any impact that it may have on the responsibilities of SC4. 
Chair: Chuck Amrhyn 

Working Group 4.9, Wire, Conductor and Cable Terminology. Subcommittee 4 created a working group 
to address the use of terms line wires, conductors, and cables. This working group was formed as a result of 
CP 2147. 
Chair: Stephen Olinick 

Working Group 4.10, New Ice Loads and Clearances. Subcommittee 4 created a working group to deal 
with pending changes in the ice loading map that will affect rules contained in Section 23. See CP 2209 and 
CP 2372. 
Chair: Larry Slavin 

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Copyright © 2001 IEEE. All rights reserved. 



I 



WORKING GROUP ASSIGNMENTS 



Subcommittee 5, Overhead Lines-Strength and Loadings (SC5) 

Working Group 5.1, Continuity of Sections 24, 25, and 26. This working group is examining the appropri- 
ate placement of requirements within Sections 24, 25, and 26 of the present code system and developing a 
basis for coordinating the relative values of present and future requirements for loading factors, material 
strength factors, importance factors, and similar requirements that will assure appropriate results from the 
present or from a possible future calculation system. 
Chair: L. Kempner 

This working group also contains the following Task Forces: 
TF 5.1.1, Load Factors. Chair: R. Kluge 

TF 5.1.4, Old/ Alternate vs Recommended Method. Chair: L. Kempner 
TF 5.1.7, Fiber Reinforced Composite Structures. Chair: N. Bingel 
TF 5.1.8, Grade B vs Grade C Reliability. Chair: N. Bingel 

Working Group 5.2, Complete Revisions of Sections 25 and 26. The scope of this work is to continue to 

review CP 2372, which deals with a major revision of Sections 24-27 (the "new method"). 

Chair: Robert C. Peters 

This working group also contains the following task forces: 

TF 5.2.1, Ice Loading. Chair: Clayton Clem 

Working Group 5.6, Line Insulation. Continuing review of overhead line insulation component 

performance, analysis of insulator problems due to component age and other factors, along with the 

recommendations for appropriate recognition of newly developing synthetic insulating components and the 

appropriate methods to test for normal and extreme loading conditions. 

Chair: Thomas A. Pinkham. 

This working group contains the following task forces: 

TF 5.6.1, Coordinate changes and improvements. Chair: T. A. Pinkham 

TF 5.6.2, Test Methods/Extreme Loading. T. A. Pinkham 

Working Group 5.7, Seminars and Presentations. A working group was set up to develop a Panel Session 

to explain the changes in the NESC 2002 Edition to industry and the public. Panel Sessions are currently 

scheduled at the Summer Power Engineering Society meeting in July, 2001, and at the Winter Transmission 

and Distribution Expo in October 2001. Other public presentations are provided, as appropriate. 

Chair: Lawrence Slavin 

TF 5.7.1, Technical Presentations, 2002 Edition. Chair: Lawrence Slavin 

TF 5.7.2, Field Surveys on Relative Impact of Proposed New and Old System, (Sections 23 and 24-27). 

Chair: Lawrence Slavin 

Working Group 5.8, Application of Extreme Wind to All Structures. A working group was set up to de- 
velop recommendations for appropriate differences in wind treatment or other limitations for lower profile 
structures and lines vs higher structures and lines for the 2007 Edition. See CP 2151 regarding evaluation of 
the 60-ft exclusion in the application of high wind loading to overhead lines. 
Chair: Donald Heald 

Subcommittee 7, Underground Lines (SC7) 

Working Group 7.5, Manholes and Vaults. SC7 created a working group to review definitions and usage 
of the terms "manholes" and "vaults." 
Chair: Les Shankland 



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Copyright © 2001 IEEE. All rights reserved. 



WORKING GROUP ASSIGNMENTS 



Subcommittee 8, Work Rules (SC8) 

Working Group 8.10, Worker Clothing. WG 8.10 was formed to address CPs 2122, 2357, 2358, and 2343. 
WG will develop a report and change proposal(s) for the 2007 Edition. 
Chair: Jim Tomaseski 



285 
Copyright © 2001 IEEE. All rights reserved. 



TENTATIVE INTERIM AMENDMENT 



Tentative Interim Amendment 2002-1 

to the 

National Electrical Safety Code 

ANSI C2-2002 



9 May 2001 



In accordance with Section 13 of its Procedures, the National Electrical Safety Code Committee has 
issued the following Tentative Interim Amendment (TIA) to ANSI C2, National Electrical Safety 
Code, 2002 Edition. The TIA was issued by the Secretariat on 9 May 2001, as a result of a proposal 
submitted by a member of the NESC Main Committee. 

A Tentative Interim Amendment is tentative because it has not been processed through the entire 
standards-making procedure. It is interim because it is effective only between editions of the code. 
A TIA automatically becomes a Proposal of the proponent for the next edition of the code; as such, 
it is then subject to all the procedures of the standards-making process. 



Rule 123C: Delete the last sentence and add the following underlined sentence, 
c. Provisions for Grounding Equipment During Maintenance. 

Electric equipment or conductors normally operating at more than 600 V between conductors, on 
or about which work is occasionally done while isolated from a source of electric energy by dis- 
connecting or isolating switches only, shall be provided with some means for grounding, such as 
switches, connectors, or a readily accessible means for connecting a portable grounding conduc- 
tor. WhefHweessa^^reuHdiflg-fflay-teeeHirtted-^^ 

and not influenced by higher voltage conductor s , where visible openings in the s ource of supply 
are available, and are properly tagged in the open position. See Part 4 of this code. 

Rule 173C: Delete entire rule. 



286 
Copyright © 2001 IEEE. All rights reserved. 



TENTATIVE INTERIM AMENDMENT 



Tentative Interim Amendment 2002-2 

to the 

National Electrical Safety Code 

ANSIC2-2002 



23 April 2001 



In accordance with Section 13 of its Procedures, the National Electrical Safety Code Committee has 
issued the following Tentative Interim Amendment (TIA) to ANSI C2, National Electrical Safety 
Code, 2002 Edition. The TIA was issued by the Secretariat on 23 April 2001, as a result of a proposal 
submitted by a member of the NESC Main Committee. 

A Tentative Interim Amendment is tentative because it has not been processed through the entire 
standards-making procedure. It is interim because it is effective only between editions of the code. 
A TIA automatically becomes a Proposal of the proponent for the next edition of the code; as such, 
it is then subject to all the procedures of the standards-making process. 



Table 232-2 m and ft are revised as follows: 

Replace footnote 1 in row lb, column 2 with unused footnote 6 in both the meter and feet Tables 232-2 thusly: 

6 This footnote not u s ed in this e dition. This clearance may be reduced to the following values for driveways, 
parking lots, and alleys not subject to truck traffic: 

meters feet 

(a) Insulated live parts limited to 300 V to ground 3Jj 12 

(b) Insulated live parts limited to 150 V to ground 3^0 10 

Also replace footnote 1(b) in row Id, column 2 with footnote 1 and revise footnote 1 thusly: 

^ This clearance may be reduced to the following values: 

meters feet 

(a) Insulated live parts limited to 300 V to ground 3t6 42 

(b) Insulated live part s limited to 150 V to ground 3^0 40 
^or insulated live parts limited to 150 V to ground, this value may be reduced to 3.0 m (10 ft). 

Since the footnote only references 1(b) making this revision eliminates the need for the present footnote 
1(a) and 1(b). 



I 



287 
Copyright © 2001 IEEE. All rights reserved. 




/- TcTReorder F i,easg Can" 
1-800-24Q-63.73 



m 



w 



L 



SH9491 1 
1 August 2001 

ISBN 0-7361-2773-7 




9 780738»127781